From ae5ab2d772eac4a16b542c0ccfbe1a4677f7da0c Mon Sep 17 00:00:00 2001
From: Thomas <28439359+thoda-dev@users.noreply.github.com>
Date: Mon, 14 Sep 2026 15:00:35 +0200
Subject: [PATCH 1/7] Run CI on Node.js 20

---
 .github/workflows/test.yml | 2 +-
 .tool-versions             | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 2f9efab..1eaec4c 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -9,7 +9,7 @@ jobs:
       - uses: actions/checkout@v2
       - uses: actions/setup-node@v3
         with:
-          node-version: 18.12.1
+          node-version: 20.20.2
           cache: 'yarn'
       - run: yarn install --frozen-lockfile
       - run: yarn lint
diff --git a/.tool-versions b/.tool-versions
index ef93526..39847f7 100644
--- a/.tool-versions
+++ b/.tool-versions
@@ -1,2 +1,2 @@
-nodejs 18.12.1
+nodejs 20.20.2
 yarn 1.22.17

From e71d5978f87b6ba21a5ea2a953f7ccf4e039fec0 Mon Sep 17 00:00:00 2001
From: Thomas <28439359+thoda-dev@users.noreply.github.com>
Date: Mon, 14 Sep 2026 15:00:35 +0200
Subject: [PATCH 2/7] Support nodemailer 10

---
 package.json                              |  4 +-
 src/__tests__/adapters/attachment.test.ts | 19 +++++
 src/__tests__/adapters/headers.test.ts    | 54 ++++++++++++++
 src/__tests__/adapters/mail.test.ts       |  8 +--
 src/__tests__/adapters/recipients.test.ts | 68 ++++++++++++++++--
 src/adapters/attachement.ts               | 16 ++---
 src/adapters/content.ts                   | 13 +++-
 src/adapters/headers.ts                   | 85 +++++++++++++++++------
 src/adapters/mail.ts                      | 13 ++--
 src/adapters/recipients.ts                | 80 +++++++++++++--------
 src/types/transport.ts                    |  2 +-
 yarn.lock                                 |  8 +--
 12 files changed, 283 insertions(+), 87 deletions(-)

diff --git a/package.json b/package.json
index d2c8c68..7d86d5c 100644
--- a/package.json
+++ b/package.json
@@ -27,7 +27,7 @@
     "eslint-plugin-import": "^2.29.1",
     "eslint-plugin-prettier": "^4.0.0",
     "jest": "^29.3.1",
-    "nodemailer": "^9.0.1",
+    "nodemailer": "^10.0.0",
     "prettier": "^2.6.2",
     "rimraf": "^5.0.5",
     "ts-node": "^10.2.1",
@@ -48,7 +48,7 @@
   },
   "peerDependencies": {
     "@types/nodemailer": "^6.4.9",
-    "nodemailer": "^9.0.1"
+    "nodemailer": "^9.0.1 || ^10.0.0"
   },
   "peerDependenciesMeta": {
     "nodemailer": {
diff --git a/src/__tests__/adapters/attachment.test.ts b/src/__tests__/adapters/attachment.test.ts
index f4a8166..cd7c4f5 100644
--- a/src/__tests__/adapters/attachment.test.ts
+++ b/src/__tests__/adapters/attachment.test.ts
@@ -1,4 +1,5 @@
 import { Readable } from "stream";
+import { readFileSync } from "node:fs";
 
 import adaptAttachment from "../../adapters/attachement";
 
@@ -91,5 +92,23 @@ describe("adapters/attachment: ", () => {
 
       expect(result).toEqual(expectedAttachment);
     });
+
+    it("returns adapted attachment object in case if content is a content object.", () => {
+      const attachment = {
+        filename: "mock-filename",
+        content: { path: __filename },
+      };
+
+      const expectedAttachment = {
+        filename: attachment.filename,
+        content: readFileSync(__filename),
+        disposition: undefined,
+        content_id: undefined,
+        type: undefined,
+      };
+      const result = adaptAttachment(attachment);
+
+      expect(result).toEqual(expectedAttachment);
+    });
   });
 });
diff --git a/src/__tests__/adapters/headers.test.ts b/src/__tests__/adapters/headers.test.ts
index 85eb40b..01c9d6e 100644
--- a/src/__tests__/adapters/headers.test.ts
+++ b/src/__tests__/adapters/headers.test.ts
@@ -61,5 +61,59 @@ describe("adapters/headers: ", () => {
 
       expect(result).toEqual(expectedResult);
     });
+
+    it("returns object if headers is a single `{ key, value }` pair.", () => {
+      const headers = {
+        key: "mock-key",
+        value: "mock-value",
+      };
+
+      const expectedResult = {
+        [headers.key]: headers.value,
+      };
+      const result = adaptHeaders(headers);
+
+      expect(result).toEqual(expectedResult);
+    });
+
+    it("converts non-string header values to strings.", () => {
+      const date = new Date("2026-01-02T03:04:05Z");
+      const headers = {
+        mockNumber: 42,
+        mockBoolean: true,
+        mockDate: date,
+        mockAddress: { name: "mock-name", address: "mock-email" },
+        mockAddressWithoutName: { address: "mock-email" },
+        mockNested: [[{ prepared: true, value: 7 }]],
+      };
+
+      const expectedResult = {
+        mockNumber: "42",
+        mockBoolean: "true",
+        mockDate: date.toUTCString(),
+        mockAddress: "mock-name <mock-email>",
+        mockAddressWithoutName: "mock-email",
+        mockNested: "7",
+      };
+      const result = adaptHeaders(headers);
+
+      expect(result).toEqual(expectedResult);
+    });
+
+    it("skips headers with empty values.", () => {
+      const headers = {
+        mockNull: null,
+        mockUndefined: undefined,
+        mockEmptyArray: [],
+        mockKey: "mock-value",
+      };
+
+      const expectedResult = {
+        mockKey: "mock-value",
+      };
+      const result = adaptHeaders(headers);
+
+      expect(result).toEqual(expectedResult);
+    });
   });
 });
diff --git a/src/__tests__/adapters/mail.test.ts b/src/__tests__/adapters/mail.test.ts
index 7c118fa..05660a4 100644
--- a/src/__tests__/adapters/mail.test.ts
+++ b/src/__tests__/adapters/mail.test.ts
@@ -3,7 +3,7 @@ import adaptMail from "../../adapters/mail";
 import config from "../../config";
 import {
   adaptSingleRecipient,
-  adaptReplyToRecipient,
+  adaptFirstRecipient,
 } from "../../adapters/recipients";
 
 const { ERRORS } = config;
@@ -37,7 +37,7 @@ describe("adapters/mail: ", () => {
         bcc: [],
         headers: data.headers,
         subject: data.subject,
-        reply_to: adaptReplyToRecipient(data.replyTo),
+        reply_to: adaptFirstRecipient(data.replyTo),
       };
       const result = adaptMail(data);
 
@@ -63,7 +63,7 @@ describe("adapters/mail: ", () => {
         bcc: [],
         headers: data.headers,
         attachments: data.attachments,
-        reply_to: adaptReplyToRecipient(data.replyTo),
+        reply_to: adaptFirstRecipient(data.replyTo),
       };
       const result = adaptMail(data);
 
@@ -93,7 +93,7 @@ describe("adapters/mail: ", () => {
         headers: data.headers,
         attachments: data.attachments,
         custom_variables: data.customVariables,
-        reply_to: adaptReplyToRecipient(data.replyTo),
+        reply_to: adaptFirstRecipient(data.replyTo),
       };
       const result = adaptMail(data);
 
diff --git a/src/__tests__/adapters/recipients.test.ts b/src/__tests__/adapters/recipients.test.ts
index b39aac1..3a18fe1 100644
--- a/src/__tests__/adapters/recipients.test.ts
+++ b/src/__tests__/adapters/recipients.test.ts
@@ -1,6 +1,6 @@
 import adaptRecipients, {
   adaptSingleRecipient,
-  adaptReplyToRecipient,
+  adaptFirstRecipient,
 } from "../../adapters/recipients";
 
 describe("adapters/recipients: ", () => {
@@ -30,6 +30,19 @@ describe("adapters/recipients: ", () => {
 
       expect(result).toEqual(expectedResult);
     });
+
+    it("omits name if Nodemailer address has no name.", () => {
+      const recipient = {
+        address: "mock-email",
+      };
+
+      const expectedResult = {
+        email: recipient.address,
+      };
+      const result = adaptSingleRecipient(recipient);
+
+      expect(result).toEqual(expectedResult);
+    });
   });
 
   describe("adaptRecipients(): ", () => {
@@ -85,14 +98,48 @@ describe("adapters/recipients: ", () => {
 
       expect(result).toEqual(expectedResult);
     });
+
+    it("flattens nested recipients arrays.", () => {
+      const recipients = [
+        "mock-email-1",
+        [{ name: "mock-name-2", address: "mock-email-2" }, ["mock-email-3"]],
+      ];
+
+      const expectedResult = [
+        { email: "mock-email-1" },
+        { name: "mock-name-2", email: "mock-email-2" },
+        { email: "mock-email-3" },
+      ];
+      const result = adaptRecipients(recipients);
+
+      expect(result).toEqual(expectedResult);
+    });
+
+    it("expands address groups into their members.", () => {
+      const recipients = {
+        name: "mock-group",
+        group: [
+          { name: "mock-name-1", address: "mock-email-1" },
+          { address: "mock-email-2" },
+        ],
+      };
+
+      const expectedResult = [
+        { name: "mock-name-1", email: "mock-email-1" },
+        { email: "mock-email-2" },
+      ];
+      const result = adaptRecipients(recipients);
+
+      expect(result).toEqual(expectedResult);
+    });
   });
 
-  describe("adaptReplyToRecipient(): ", () => {
+  describe("adaptFirstRecipient(): ", () => {
     it("returns undefined if recipients is invalid.", () => {
       const recipients = undefined;
 
       const expectedResult = undefined;
-      const result = adaptReplyToRecipient(recipients);
+      const result = adaptFirstRecipient(recipients);
 
       expect(result).toEqual(expectedResult);
     });
@@ -101,7 +148,7 @@ describe("adapters/recipients: ", () => {
       const recipients: any = [];
 
       const expectedResult = undefined;
-      const result = adaptReplyToRecipient(recipients);
+      const result = adaptFirstRecipient(recipients);
 
       expect(result).toEqual(expectedResult);
     });
@@ -116,7 +163,7 @@ describe("adapters/recipients: ", () => {
         name: recipients.name,
         email: recipients.address,
       };
-      const result = adaptReplyToRecipient(recipients);
+      const result = adaptFirstRecipient(recipients);
 
       expect(result).toEqual(expectedResult);
     });
@@ -137,7 +184,16 @@ describe("adapters/recipients: ", () => {
         name: recipients[0].name,
         email: recipients[0].address,
       };
-      const result = adaptReplyToRecipient(recipients);
+      const result = adaptFirstRecipient(recipients);
+
+      expect(result).toEqual(expectedResult);
+    });
+
+    it("returns first adapted recipient if it's a nested array.", () => {
+      const recipients = [[], ["mock-email-1", "mock-email-2"]];
+
+      const expectedResult = { email: "mock-email-1" };
+      const result = adaptFirstRecipient(recipients);
 
       expect(result).toEqual(expectedResult);
     });
diff --git a/src/adapters/attachement.ts b/src/adapters/attachement.ts
index b1321e7..4257589 100644
--- a/src/adapters/attachement.ts
+++ b/src/adapters/attachement.ts
@@ -1,16 +1,20 @@
-import { Attachment as NodemailerAttachment } from "nodemailer/lib/mailer";
+import Mail from "nodemailer/lib/mailer";
+
+import adaptContent from "./content";
 
 import CONFIG from "../config";
 
 import { Attachment } from "../types/mailtrap";
 
+type NodemailerAttachment = Mail.Attachment;
+
 const { ERRORS } = CONFIG;
 const { FILENAME_REQUIRED, CONTENT_REQUIRED } = ERRORS;
 
 /**
  * Adopts Nodemailer attachment to Mailtrap.
  * Checks if filename or content are missing, then rejects with error.
- * Otherwise specifies type of content, then builds attachment object for Mailtrap.
+ * Otherwise adapts the content, then builds attachment object for Mailtrap.
  * @todo throw error when only filename is provided
  */
 export default function adaptAttachment(
@@ -24,15 +28,9 @@ export default function adaptAttachment(
     throw new Error(CONTENT_REQUIRED);
   }
 
-  const content =
-    typeof nodemailerAttachment.content === "string" ||
-    nodemailerAttachment.content instanceof Buffer
-      ? nodemailerAttachment.content
-      : nodemailerAttachment.content.read();
-
   return {
     filename: nodemailerAttachment.filename,
-    content,
+    content: adaptContent(nodemailerAttachment.content),
     disposition: nodemailerAttachment.contentDisposition,
     content_id: nodemailerAttachment.cid,
     type: nodemailerAttachment.contentType,
diff --git a/src/adapters/content.ts b/src/adapters/content.ts
index da47a17..6aa2fd4 100644
--- a/src/adapters/content.ts
+++ b/src/adapters/content.ts
@@ -1,6 +1,15 @@
 import { readFileSync } from "node:fs";
 import { Readable } from "node:stream";
-import { AttachmentLike } from "nodemailer/lib/mailer";
+
+/**
+ * Content as nodemailer accepts it for `text`, `html` and attachments: a string, a Buffer, a readable stream or an object pointing to the content.
+ */
+export type NodemailerContent = string | Buffer | Readable | ContentObject;
+
+interface ContentObject {
+  content?: NodemailerContent | undefined;
+  path?: unknown;
+}
 
 /**
  * Checks if content type is rather string or buffer, returns content.
@@ -9,7 +18,7 @@ import { AttachmentLike } from "nodemailer/lib/mailer";
  * Otherwise reads file.
  */
 export default function adaptContent(
-  content: string | Buffer | Readable | AttachmentLike
+  content: NodemailerContent
 ): string | Buffer {
   if (typeof content === "string" || content instanceof Buffer) {
     return content;
diff --git a/src/adapters/headers.ts b/src/adapters/headers.ts
index 526d85f..3245d76 100644
--- a/src/adapters/headers.ts
+++ b/src/adapters/headers.ts
@@ -1,42 +1,83 @@
-import { Headers } from "nodemailer/lib/mailer";
+import Mail from "nodemailer/lib/mailer";
 
 import { MailtrapHeaders } from "../types/mailtrap";
 
+type Headers = Mail.Headers;
+
 /**
- * Adapts nodemailer headers to mailtrap compatible form.
- * If `nodemailerHeaders` is array of { key, value } objects, then converts to object.
- * Otherwise if value is string, keeps as is. If it's an array, first value.
+ * Converts a single nodemailer header value to a string.
+ * Nodemailer accepts strings, numbers, booleans, dates, address objects, `{ prepared, value }` objects and arrays of these. Returns `undefined`
+ * for empty values so the header gets skipped.
  * @todo support multiple value per header
  */
-export default function adaptHeaders(
-  nodemailerHeaders: Headers
-): MailtrapHeaders {
-  if (Array.isArray(nodemailerHeaders)) {
-    return nodemailerHeaders.reduce((acc, header) => {
-      acc[header.key] = header.value;
+function adaptHeaderValue(value: unknown): string | undefined {
+  if (value === null || value === undefined) {
+    return undefined;
+  }
 
-      return acc;
-    }, {} as MailtrapHeaders);
+  if (typeof value === "string") {
+    return value;
   }
 
-  const headerKeys = Object.keys(nodemailerHeaders);
+  if (typeof value === "number" || typeof value === "boolean") {
+    return String(value);
+  }
+
+  if (value instanceof Date) {
+    return value.toUTCString();
+  }
+
+  if (Array.isArray(value)) {
+    return adaptHeaderValue(value[0]); // TODO: support multiple value per header
+  }
+
+  if (typeof value === "object") {
+    if ("value" in value) {
+      return adaptHeaderValue(value.value);
+    }
+
+    if ("address" in value) {
+      const { name, address } = value as Mail.Address;
 
-  return headerKeys.reduce((acc, key) => {
-    const value = nodemailerHeaders[key];
+      return name ? `${name} <${address ?? ""}>` : address;
+    }
+  }
 
-    if (typeof value === "string") {
-      acc[key] = value;
+  return undefined;
+}
 
-      return acc;
+/**
+ * Adapts nodemailer headers to mailtrap compatible form.
+ * If `nodemailerHeaders` is a { key, value } object or an array of them, then converts to object.
+ * Otherwise iterates over the object keys, converting each value to string.
+ */
+export default function adaptHeaders(
+  nodemailerHeaders: Headers
+): MailtrapHeaders {
+  const entries: Array<[string, unknown]> = (() => {
+    if (Array.isArray(nodemailerHeaders)) {
+      return nodemailerHeaders.map(({ key, value }) => [key, value]);
     }
 
-    if (Array.isArray(value)) {
-      [acc[key]] = value; // TODO: support multiple value per header
+    // Single `{ key, value }` header, handled the same way nodemailer does in `setHeader`.
+    const { key, value } = nodemailerHeaders as {
+      key?: unknown;
+      value?: unknown;
+    };
 
-      return acc;
+    if (typeof key === "string" && "value" in nodemailerHeaders) {
+      return [[key, value]];
     }
 
-    acc[key] = value.value;
+    return Object.entries(nodemailerHeaders);
+  })();
+
+  return entries.reduce((acc, [key, value]) => {
+    const adaptedValue = adaptHeaderValue(value);
+
+    if (adaptedValue !== undefined) {
+      acc[key] = adaptedValue;
+    }
 
     return acc;
   }, {} as MailtrapHeaders);
diff --git a/src/adapters/mail.ts b/src/adapters/mail.ts
index 547001e..0f20c81 100644
--- a/src/adapters/mail.ts
+++ b/src/adapters/mail.ts
@@ -1,10 +1,7 @@
 import adaptAttachment from "./attachement";
 import adaptContent from "./content";
 import adaptHeaders from "./headers";
-import adaptRecipients, {
-  adaptSingleRecipient,
-  adaptReplyToRecipient,
-} from "./recipients";
+import adaptRecipients, { adaptFirstRecipient } from "./recipients";
 
 import CONFIG from "../config";
 
@@ -21,16 +18,18 @@ const { SUBJECT_REQUIRED, FROM_REQUIRED } = ERRORS;
  * Then returns mail with all params needed.
  */
 export default function adaptMail(data: MailtrapMailOptions): Mail | SendError {
-  if (!data.from) {
+  const from = adaptFirstRecipient(data.from);
+
+  if (!from) {
     return { success: false, errors: [FROM_REQUIRED] };
   }
 
   const mail: CommonMail = {
-    from: adaptSingleRecipient(data.from),
+    from,
     to: adaptRecipients(data.to),
     cc: adaptRecipients(data.cc),
     bcc: adaptRecipients(data.bcc),
-    reply_to: adaptReplyToRecipient(data.replyTo),
+    reply_to: adaptFirstRecipient(data.replyTo),
   };
 
   if (data.headers) {
diff --git a/src/adapters/recipients.ts b/src/adapters/recipients.ts
index 458122e..37f5fb4 100644
--- a/src/adapters/recipients.ts
+++ b/src/adapters/recipients.ts
@@ -1,10 +1,43 @@
-import { Address as NodemailerAddress } from "nodemailer/lib/mailer";
-
 import { Address } from "../types/mailtrap";
 
+/**
+ * Address object as nodemailer accepts it. Declared structurally so it matches both the types bundled with nodemailer >= 10 and `@types/nodemailer`.
+ */
+type NodemailerAddress = {
+  name?: string | undefined;
+  address?: string | undefined;
+  group?: NodemailerAddress[] | undefined;
+};
+
+/**
+ * Recipients as nodemailer accepts them: a string, an address object, or an array of these (nested arrays included).
+ */
+export type NodemailerRecipients =
+  | string
+  | NodemailerAddress
+  | NodemailerRecipients[];
+
+/**
+ * Flattens nodemailer recipients into a plain list of string or address objects.
+ * Address groups (`{ name, group: [...] }`) are expanded into their members.
+ */
+function flattenRecipients(
+  recipients: NodemailerRecipients
+): Array<string | NodemailerAddress> {
+  if (Array.isArray(recipients)) {
+    return recipients.flatMap(flattenRecipients);
+  }
+
+  if (typeof recipients !== "string" && recipients.group) {
+    return flattenRecipients(recipients.group);
+  }
+
+  return [recipients];
+}
+
 /**
  * If type of `recipient` is string, then wraps it into email object.
- * Otherwise maps into { `name`, `email` } pair.
+ * Otherwise maps into { `name`, `email` } pair, `name` being optional in nodemailer.
  */
 export function adaptSingleRecipient(
   recipient: string | NodemailerAddress
@@ -13,52 +46,39 @@ export function adaptSingleRecipient(
     return { email: recipient };
   }
 
-  return { name: recipient.name, email: recipient.address };
+  return {
+    ...(recipient.name !== undefined && { name: recipient.name }),
+    email: recipient.address ?? "",
+  };
 }
 
 /**
  * If there is no recipient, then returns empty array.
- * If it's not array, then adopts recipient and wraps into array.
- * Otherwise maps trough recipients and adopts each one for Mailtrap.
+ * Otherwise flattens recipients and adopts each one for Mailtrap.
  */
 export default function adaptRecipients(
-  recipients:
-    | string
-    | NodemailerAddress
-    | Array<string | NodemailerAddress>
-    | undefined
+  recipients: NodemailerRecipients | undefined
 ): Address[] {
   if (!recipients) {
     return [];
   }
 
-  if (!Array.isArray(recipients)) {
-    return [adaptSingleRecipient(recipients)];
-  }
-
-  return recipients.map(adaptSingleRecipient);
+  return flattenRecipients(recipients).map(adaptSingleRecipient);
 }
 
 /**
  * If there is no recipient or empty array is passed, then return undefined since it is an optional field.
- * If it's not array, then adapt recipient and returns it.
- * Otherwise, if type is array as nodemailer allows, we pick the first recipient
- * as Mailtrap doesn't support multiple reply-to recipients.
+ * Otherwise, if several recipients are given as nodemailer allows, we pick the first one.
+ * Used for `from` and `reply_to` as Mailtrap supports a single address for both.
  */
-export function adaptReplyToRecipient(
-  recipients:
-    | string
-    | NodemailerAddress
-    | Array<string | NodemailerAddress>
-    | undefined
+export function adaptFirstRecipient(
+  recipients: NodemailerRecipients | undefined
 ): Address | undefined {
-  if (!recipients || (Array.isArray(recipients) && recipients.length === 0)) {
+  if (!recipients) {
     return undefined;
   }
 
-  if (!Array.isArray(recipients)) {
-    return adaptSingleRecipient(recipients);
-  }
+  const [first] = flattenRecipients(recipients);
 
-  return adaptSingleRecipient(recipients[0]);
+  return first === undefined ? undefined : adaptSingleRecipient(first);
 }
diff --git a/src/types/transport.ts b/src/types/transport.ts
index c01468a..7a391f6 100644
--- a/src/types/transport.ts
+++ b/src/types/transport.ts
@@ -1,4 +1,4 @@
-import NodemailerMail = require("nodemailer/lib/mailer");
+import NodemailerMail from "nodemailer/lib/mailer";
 
 import { Transport, Transporter } from "nodemailer";
 import {
diff --git a/yarn.lock b/yarn.lock
index 4a718fc..89f5926 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -4003,10 +4003,10 @@ node-releases@^2.0.53:
   resolved "https://registry.yarnpkg.com/node-releases/-/node-releases-2.0.54.tgz#09af17d5647aa9f221ec5cf2becb95b68a981afe"
   integrity sha512-YHs7BmmcsdAI5Ozuf8JZo6PT0mv2GIWC9vMfvUC3dp65M8hn7Ux8CPL+2oBI7juNuj9d0ndhTcznq2ODBps9cQ==
 
-nodemailer@^9.0.1:
-  version "9.0.1"
-  resolved "https://registry.yarnpkg.com/nodemailer/-/nodemailer-9.0.1.tgz#871c04d8423fc0c790289f4a8f6f71f1b3563e8c"
-  integrity sha512-Gwv8SQewT616ZM/URn0H54b8PWo/Wum7md3EW2aWy1lO27+WZCX+Xyak3J+NlmHUjDh5ME+uesJUDRbR3Ye8Bw==
+nodemailer@^10.0.0:
+  version "10.0.9"
+  resolved "https://registry.yarnpkg.com/nodemailer/-/nodemailer-10.0.9.tgz#1860325627921b3c6e160d941f5d525ff9a8ca1e"
+  integrity sha512-BF0qcyplCwp+jMk6HCjFykBz/YhhZSsxrARhOldLwFWH+8kGjQsd2WIMIZhqEuyXRoGFi0ONbDeWDMDoL8MhLw==
 
 normalize-path@^3.0.0:
   version "3.0.0"

From 4ea431862d5b20526e3e8ef0f25442b65280a214 Mon Sep 17 00:00:00 2001
From: Thomas <28439359+thoda-dev@users.noreply.github.com>
Date: Mon, 14 Sep 2026 15:00:35 +0200
Subject: [PATCH 3/7] Document nodemailer 10 support in README

---
 README.md | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/README.md b/README.md
index 39750c1..ad0d92e 100644
--- a/README.md
+++ b/README.md
@@ -198,7 +198,7 @@ mailtrap
 
 ## Nodemailer Transport
 
-> NOTE: [Nodemailer](https://www.npmjs.com/package/nodemailer) is needed as a dependency.
+> NOTE: [Nodemailer](https://www.npmjs.com/package/nodemailer) is needed as a dependency. Versions 9 and 10 are supported (Nodemailer 10 requires Node.js 20 or newer).
 
 ```sh
 npm install nodemailer
@@ -207,7 +207,7 @@ npm install nodemailer
 yarn add nodemailer
 ```
 
-If you're using TypeScript, install `@types/nodemailer` as a `devDependency`:
+If you're using TypeScript with Nodemailer 9, install `@types/nodemailer` as a `devDependency` (Nodemailer 10 ships its own type definitions, so this is not needed there):
 
 ```sh
 npm install -D @types/nodemailer

From a27b91ff08c4d7a648cfdc21d67dabaf71c1e8a7 Mon Sep 17 00:00:00 2001
From: Thomas <28439359+thoda-dev@users.noreply.github.com>
Date: Mon, 14 Sep 2026 15:12:58 +0200
Subject: [PATCH 4/7] Move nodemailer input types to transport types

---
 src/adapters/content.ts    | 10 +---------
 src/adapters/recipients.ts | 18 +-----------------
 src/types/transport.ts     | 35 +++++++++++++++++++++++++++++++++++
 3 files changed, 37 insertions(+), 26 deletions(-)

diff --git a/src/adapters/content.ts b/src/adapters/content.ts
index 6aa2fd4..ee900d7 100644
--- a/src/adapters/content.ts
+++ b/src/adapters/content.ts
@@ -1,15 +1,7 @@
 import { readFileSync } from "node:fs";
 import { Readable } from "node:stream";
 
-/**
- * Content as nodemailer accepts it for `text`, `html` and attachments: a string, a Buffer, a readable stream or an object pointing to the content.
- */
-export type NodemailerContent = string | Buffer | Readable | ContentObject;
-
-interface ContentObject {
-  content?: NodemailerContent | undefined;
-  path?: unknown;
-}
+import { NodemailerContent } from "../types/transport";
 
 /**
  * Checks if content type is rather string or buffer, returns content.
diff --git a/src/adapters/recipients.ts b/src/adapters/recipients.ts
index 37f5fb4..a1acc8e 100644
--- a/src/adapters/recipients.ts
+++ b/src/adapters/recipients.ts
@@ -1,21 +1,5 @@
 import { Address } from "../types/mailtrap";
-
-/**
- * Address object as nodemailer accepts it. Declared structurally so it matches both the types bundled with nodemailer >= 10 and `@types/nodemailer`.
- */
-type NodemailerAddress = {
-  name?: string | undefined;
-  address?: string | undefined;
-  group?: NodemailerAddress[] | undefined;
-};
-
-/**
- * Recipients as nodemailer accepts them: a string, an address object, or an array of these (nested arrays included).
- */
-export type NodemailerRecipients =
-  | string
-  | NodemailerAddress
-  | NodemailerRecipients[];
+import { NodemailerAddress, NodemailerRecipients } from "../types/transport";
 
 /**
  * Flattens nodemailer recipients into a plain list of string or address objects.
diff --git a/src/types/transport.ts b/src/types/transport.ts
index 7a391f6..1b3aca2 100644
--- a/src/types/transport.ts
+++ b/src/types/transport.ts
@@ -1,5 +1,6 @@
 import NodemailerMail from "nodemailer/lib/mailer";
 
+import { Readable } from "node:stream";
 import { Transport, Transporter } from "nodemailer";
 import {
   SendResponse,
@@ -8,6 +9,40 @@ import {
   TemplateVariables,
 } from "./mailtrap";
 
+/**
+ * Address object as nodemailer accepts it. Declared structurally so it matches both the types bundled with nodemailer >= 10 and `@types/nodemailer`.
+ */
+export type NodemailerAddress = {
+  name?: string | undefined;
+  address?: string | undefined;
+  group?: NodemailerAddress[] | undefined;
+};
+
+/**
+ * Recipients as nodemailer accepts them: a string, an address object, or an array of these (nested arrays included).
+ */
+export type NodemailerRecipients =
+  | string
+  | NodemailerAddress
+  | NodemailerRecipients[];
+
+/**
+ * Object pointing to a content instead of carrying it.
+ */
+type NodemailerContentObject = {
+  content?: NodemailerContent | undefined;
+  path?: unknown;
+};
+
+/**
+ * Content as nodemailer accepts it for `text`, `html` and attachments: a string, a Buffer, a readable stream or an object pointing to the content.
+ */
+export type NodemailerContent =
+  | string
+  | Buffer
+  | Readable
+  | NodemailerContentObject;
+
 type AdditionalFields = {
   category?: string;
   custom_variables?: CustomVariables;

From 8e7b19168047ecea9a7d20dbc83cb0f7053d4d3e Mon Sep 17 00:00:00 2001
From: Thomas <28439359+thoda-dev@users.noreply.github.com>
Date: Mon, 14 Sep 2026 15:35:11 +0200
Subject: [PATCH 5/7] Reject empty addresses in from and headers

---
 src/__tests__/adapters/headers.test.ts |  1 +
 src/__tests__/adapters/mail.test.ts    | 11 +++++++++++
 src/adapters/headers.ts                |  6 +++++-
 src/adapters/mail.ts                   |  2 +-
 4 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/src/__tests__/adapters/headers.test.ts b/src/__tests__/adapters/headers.test.ts
index 01c9d6e..2369a75 100644
--- a/src/__tests__/adapters/headers.test.ts
+++ b/src/__tests__/adapters/headers.test.ts
@@ -105,6 +105,7 @@ describe("adapters/headers: ", () => {
         mockNull: null,
         mockUndefined: undefined,
         mockEmptyArray: [],
+        mockAddressWithoutAddress: { name: "mock-name" },
         mockKey: "mock-value",
       };
 
diff --git a/src/__tests__/adapters/mail.test.ts b/src/__tests__/adapters/mail.test.ts
index 05660a4..5bf2331 100644
--- a/src/__tests__/adapters/mail.test.ts
+++ b/src/__tests__/adapters/mail.test.ts
@@ -20,6 +20,17 @@ describe("adapters/mail: ", () => {
       expect(result).toEqual(expectedResult);
     });
 
+    it("returns object with error `from is required` if from has no address.", () => {
+      const expectedResult = { success: false, errors: [FROM_REQUIRED] };
+
+      expect(adaptMail({ from: "" })).toEqual(expectedResult);
+      expect(adaptMail({ from: [] })).toEqual(expectedResult);
+      expect(adaptMail({ from: { address: "" } })).toEqual(expectedResult);
+      expect(adaptMail({ from: { name: "mock-name" } })).toEqual(
+        expectedResult
+      );
+    });
+
     it("returns `mail` object with basic info + headers.", () => {
       const data = {
         from: "mock-from",
diff --git a/src/adapters/headers.ts b/src/adapters/headers.ts
index 3245d76..e5818f5 100644
--- a/src/adapters/headers.ts
+++ b/src/adapters/headers.ts
@@ -39,7 +39,11 @@ function adaptHeaderValue(value: unknown): string | undefined {
     if ("address" in value) {
       const { name, address } = value as Mail.Address;
 
-      return name ? `${name} <${address ?? ""}>` : address;
+      if (!address) {
+        return undefined;
+      }
+
+      return name ? `${name} <${address}>` : address;
     }
   }
 
diff --git a/src/adapters/mail.ts b/src/adapters/mail.ts
index 0f20c81..1256b21 100644
--- a/src/adapters/mail.ts
+++ b/src/adapters/mail.ts
@@ -20,7 +20,7 @@ const { SUBJECT_REQUIRED, FROM_REQUIRED } = ERRORS;
 export default function adaptMail(data: MailtrapMailOptions): Mail | SendError {
   const from = adaptFirstRecipient(data.from);
 
-  if (!from) {
+  if (!from?.email) {
     return { success: false, errors: [FROM_REQUIRED] };
   }
 

From d3feae79d67de7a1320f81690c441cb3468207a4 Mon Sep 17 00:00:00 2001
From: Thomas <28439359+thoda-dev@users.noreply.github.com>
Date: Mon, 14 Sep 2026 16:16:02 +0200
Subject: [PATCH 6/7] Trim header addresses and narrow content path type

---
 src/__tests__/adapters/headers.test.ts | 1 +
 src/adapters/headers.ts                | 5 +++--
 src/types/transport.ts                 | 3 ++-
 3 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/src/__tests__/adapters/headers.test.ts b/src/__tests__/adapters/headers.test.ts
index 2369a75..7ddfea9 100644
--- a/src/__tests__/adapters/headers.test.ts
+++ b/src/__tests__/adapters/headers.test.ts
@@ -106,6 +106,7 @@ describe("adapters/headers: ", () => {
         mockUndefined: undefined,
         mockEmptyArray: [],
         mockAddressWithoutAddress: { name: "mock-name" },
+        mockAddressWithBlankAddress: { name: "mock-name", address: "  " },
         mockKey: "mock-value",
       };
 
diff --git a/src/adapters/headers.ts b/src/adapters/headers.ts
index e5818f5..14bf6be 100644
--- a/src/adapters/headers.ts
+++ b/src/adapters/headers.ts
@@ -38,12 +38,13 @@ function adaptHeaderValue(value: unknown): string | undefined {
 
     if ("address" in value) {
       const { name, address } = value as Mail.Address;
+      const email = address?.trim();
 
-      if (!address) {
+      if (!email) {
         return undefined;
       }
 
-      return name ? `${name} <${address}>` : address;
+      return name ? `${name} <${email}>` : email;
     }
   }
 
diff --git a/src/types/transport.ts b/src/types/transport.ts
index 1b3aca2..db9cc2d 100644
--- a/src/types/transport.ts
+++ b/src/types/transport.ts
@@ -1,6 +1,7 @@
 import NodemailerMail from "nodemailer/lib/mailer";
 
 import { Readable } from "node:stream";
+import { Url } from "node:url";
 import { Transport, Transporter } from "nodemailer";
 import {
   SendResponse,
@@ -31,7 +32,7 @@ export type NodemailerRecipients =
  */
 type NodemailerContentObject = {
   content?: NodemailerContent | undefined;
-  path?: unknown;
+  path?: string | false | Url | undefined;
 };
 
 /**

From 513692e96edc60b2a138e75f3549adcc576cab2f Mon Sep 17 00:00:00 2001
From: Thomas <28439359+thoda-dev@users.noreply.github.com>
Date: Mon, 21 Sep 2026 18:40:54 +0200
Subject: [PATCH 7/7] Reject empty adapted attachment content

---
 src/__tests__/adapters/attachment.test.ts | 15 +++++++++++++++
 src/adapters/attachement.ts               |  8 +++++++-
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/src/__tests__/adapters/attachment.test.ts b/src/__tests__/adapters/attachment.test.ts
index cd7c4f5..011f964 100644
--- a/src/__tests__/adapters/attachment.test.ts
+++ b/src/__tests__/adapters/attachment.test.ts
@@ -28,6 +28,21 @@ describe("adapters/attachment: ", () => {
       );
     });
 
+    it("throws `content required` error if adapted content is empty.", () => {
+      const emptyStream = new Readable({
+        read() {
+          this.push(null);
+        },
+      });
+
+      expect(() =>
+        adaptAttachment({ filename: "mock-filename", content: "" })
+      ).toThrowError(new Error(CONTENT_REQUIRED));
+      expect(() =>
+        adaptAttachment({ filename: "mock-filename", content: emptyStream })
+      ).toThrowError(new Error(CONTENT_REQUIRED));
+    });
+
     it("returns adapted attachment object in case if content is buffer.", () => {
       const attachment = {
         filename: "mock-filename",
diff --git a/src/adapters/attachement.ts b/src/adapters/attachement.ts
index 4257589..e12f159 100644
--- a/src/adapters/attachement.ts
+++ b/src/adapters/attachement.ts
@@ -28,9 +28,15 @@ export default function adaptAttachment(
     throw new Error(CONTENT_REQUIRED);
   }
 
+  const content = adaptContent(nodemailerAttachment.content);
+
+  if (!content) {
+    throw new Error(CONTENT_REQUIRED);
+  }
+
   return {
     filename: nodemailerAttachment.filename,
-    content: adaptContent(nodemailerAttachment.content),
+    content,
     disposition: nodemailerAttachment.contentDisposition,
     content_id: nodemailerAttachment.cid,
     type: nodemailerAttachment.contentType,