From c2c8f934c537c3a93e2194d05f28133bb9c00d6e Mon Sep 17 00:00:00 2001
From: abp <abp@tutao.de>
Date: Tue, 11 Nov 2025 14:18:50 +0100
Subject: [PATCH] add support for Q-encoded list unsubscribe headers

We now successfully parse MIME Q-encoded list unsubscribe headers and
can unsubscribe from such newsletters.
---
 src/mail-app/mail/view/MailViewerViewModel.ts | 34 ++++++++++++-------
 .../mail/view/MailViewerViewModelTest.ts      | 12 +++++++
 2 files changed, 34 insertions(+), 12 deletions(-)

diff --git a/src/mail-app/mail/view/MailViewerViewModel.ts b/src/mail-app/mail/view/MailViewerViewModel.ts
index 991145f410..bd5e561c80 100644
--- a/src/mail-app/mail/view/MailViewerViewModel.ts
+++ b/src/mail-app/mail/view/MailViewerViewModel.ts
@@ -675,6 +675,20 @@ export class MailViewerViewModel {
 		return !isEmpty(listUnsubscribeHeaders)
 	}
 
+	private decodeMimeHeader(value: string): string {
+		return value.replace(/=\?([^?]+)\?([QB])\?([^?]+)\?=/gi, (_, _charset, encoding, encodedText) => {
+			if (encoding.toUpperCase() === "Q") {
+				return encodedText.replace(/_/g, " ").replace(/=([A-Fa-f0-9]{2})/g, (_: string, hex: string) => String.fromCharCode(parseInt(hex, 16)))
+			} else if (encoding.toUpperCase() === "B") {
+				try {
+					return Buffer.from(encodedText, "base64").toString("utf-8")
+				} catch {
+					return encodedText
+				}
+			}
+			return encodedText
+		})
+	}
 	async determineUnsubscribeOrder(): Promise<Array<UnsubscribeAction>> {
 		const mailHeaders = await this.getHeaders()
 		const unsubscribeActions: Array<UnsubscribeAction> = []
@@ -682,23 +696,19 @@ export class MailViewerViewModel {
 			return unsubscribeActions
 		}
 
-		const listUnsubscribeHeaders = mailHeaders
-			.replaceAll(/\r\n/g, "\n") // replace all CR LF with LF
-			.replaceAll(/\n[ \t]/g, "") // join multiline headers to a single line
-			.split("\n") // split headers
-			.filter((headerLine) => headerLine.toLowerCase().startsWith("list-unsubscribe:"))
+		const normalizedHeaders = mailHeaders
+			.replaceAll(/\r\n/g, "\n")
+			.replaceAll(/\n[ \t]/g, "")
+			.split("\n")
+			.map((h) => this.decodeMimeHeader(h.trim()))
+
+		const listUnsubscribeHeaders = normalizedHeaders.filter((headerLine) => headerLine.toLowerCase().startsWith("list-unsubscribe:"))
 
 		if (isEmpty(listUnsubscribeHeaders)) {
 			return unsubscribeActions
 		}
 
-		const unsubPostHeader = first(
-			mailHeaders
-				.replaceAll(/\r\n/g, "\n") // replace all CR LF with LF
-				.replaceAll(/\n[ \t]/g, "") // join multiline headers to a single line
-				.split("\n") // split headers
-				.filter((headerLine) => headerLine.toLowerCase().startsWith("list-unsubscribe-post")),
-		)
+		const unsubPostHeader = normalizedHeaders.find((h) => h.toLowerCase().startsWith("list-unsubscribe-post"))
 
 		const [_, ...value] = listUnsubscribeHeaders[0].split(":")
 		const headerValue = value.join(":")
diff --git a/test/tests/mail/view/MailViewerViewModelTest.ts b/test/tests/mail/view/MailViewerViewModelTest.ts
index 5b75061ef0..ecdf47d3bd 100644
--- a/test/tests/mail/view/MailViewerViewModelTest.ts
+++ b/test/tests/mail/view/MailViewerViewModelTest.ts
@@ -306,6 +306,18 @@ o.spec("MailViewerViewModel", function () {
 				const expectedPostUrl = "http://unsub.me?id=2134"
 				await testHeaderUnsubscribePost(headers.join("\r\n"), expectedPostUrl, true)
 			})
+			o("with Q encoded header", async function () {
+				const headers = [
+					"List-Unsubscribe: ",
+					" =?us-ascii?Q?=3Chttps=3A=2F=2Fnewsletter=2Eexample=2Ecom=2Funsubscribe=2Fabcd1234efgh?=",
+					" =?us-ascii?Q?5678ijkl91011mnopqr=3E?=",
+					"List-Unsubscribe-Post: List-Unsubscribe=One-Click",
+				]
+
+				const expectedPostUrl = "https://newsletter.example.com/unsubscribe/abcd1234efgh5678ijkl91011mnopqr"
+
+				await testHeaderUnsubscribePost(headers.join("\r\n"), expectedPostUrl, true)
+			})
 			o("no list unsubscribe header", async function () {
 				const headers = "To: InvalidHeader"
 				const viewModel = initUnsubscribeHeaders(headers)