Implement Reply-To header support when replying

The Reply-To header, if present, will take precedence over the From
header. If the Reply-To data is undefined old behaviour is used.

Note that Horde libraries appear to internally determine reply_to
property in the Horde_Imap_Client_Data_Envelope (unless Dovecot does it,
but doubt). It was observed that reply_to property had the same value as
from property in a mail that contained no Reply-To header. It is assumed
that the Horde implementation makes sense, so just use the value as-is.

This notably fixes replying to mail from software reliant on the
Reply-To header such as GitLab and GitHub notifications and many types
of mail based ticketing (support) systems.

Signed-off-by: Melvin Vermeeren <[email protected]>

lib/Model/IMAPMessage.php

@@ -528,6 +528,7 @@ public function jsonSerialize() {
 			'messageId' => $this->getMessageId(),
 			'from' => $this->getFrom()->jsonSerialize(),
 			'to' => $this->getTo()->jsonSerialize(),
+			'replyTo' => $this->getReplyTo()->jsonSerialize(),
 			'cc' => $this->getCC()->jsonSerialize(),
 			'bcc' => $this->getBCC()->jsonSerialize(),
 			'subject' => $this->getSubject(),
@@ -739,17 +740,19 @@ public function setInReplyTo(string $id) {
 	/**
 	 * @return AddressList
 	 */
-	public function getReplyTo() {
+	public function getReplyTo(): AddressList {
 		return AddressList::fromHorde($this->getEnvelope()->reply_to);
 	}
 
 	/**
-	 * @param string $id
+	 * @param AddressList $replyTo
+	 *
+	 * @throws Exception
 	 *
 	 * @return void
 	 */
-	public function setReplyTo(string $id) {
-		throw new Exception('not implemented');
+	public function setReplyTo(AddressList $replyTo) {
+		throw new Exception('IMAP message is immutable');
 	}
 
 	/**

lib/Model/IMessage.php

@@ -69,6 +69,16 @@ public function getTo(): AddressList;
 	 */
 	public function setTo(AddressList $to);
 
+	/**
+	 * @return AddressList
+	 */
+	public function getReplyTo(): AddressList;
+
+	/**
+	 * @param AddressList $replyTo
+	 */
+	public function setReplyTo(AddressList $replyTo);
+
 	/**
 	 * @return AddressList
 	 */

lib/Model/Message.php

@@ -42,6 +42,9 @@ class Message implements IMessage {
 	/** @var AddressList */
 	private $to;
 
+	/** @var AddressList */
+	private $replyTo;
+
 	/** @var AddressList */
 	private $cc;
 
@@ -63,6 +66,7 @@ class Message implements IMessage {
 	public function __construct() {
 		$this->from = new AddressList();
 		$this->to = new AddressList();
+		$this->replyTo = new AddressList();
 		$this->cc = new AddressList();
 		$this->bcc = new AddressList();
 	}
@@ -126,6 +130,22 @@ public function setTo(AddressList $to) {
 		$this->to = $to;
 	}
 
+	/**
+	 * @return AddressList
+	 */
+	public function getReplyTo(): AddressList {
+		return $this->replyTo;
+	}
+
+	/**
+	 * @param AddressList $replyTo
+	 *
+	 * @return void
+	 */
+	public function setReplyTo(AddressList $replyTo) {
+		$this->replyTo = $replyTo;
+	}
+
 	/**
 	 * @return AddressList
 	 */

src/ReplyBuilder.js

@@ -73,11 +73,15 @@ const RecipientType = Object.seal({
 	Cc: 2,
 })
 
-export const buildRecipients = (envelope, ownAddress) => {
+export const buildRecipients = (envelope, ownAddress, replyTo) => {
 	let recipientType = RecipientType.None
 	const isOwnAddress = (a) => a.email === ownAddress.email
 	const isNotOwnAddress = negate(isOwnAddress)
 
+	// The Reply-To header has higher precedence than the From header.
+	// This re-uses Horde's handling of the reply_to field directly.
+	const from = replyTo !== undefined ? replyTo : envelope.from
+
 	// Locate why we received this envelope
 	// Can be in 'to', 'cc' or unknown
 	let replyingAddress = envelope.to.find(isOwnAddress)
@@ -97,28 +101,28 @@ export const buildRecipients = (envelope, ownAddress) => {
 	if (recipientType === RecipientType.To) {
 		// Send to everyone except yourself, plus the original sender if not ourself
 		to = envelope.to.filter(isNotOwnAddress)
-		to = to.concat(envelope.from.filter(isNotOwnAddress))
+		to = to.concat(from.filter(isNotOwnAddress))
 
 		// CC remains the same
 		cc = envelope.cc
 	} else if (recipientType === RecipientType.Cc) {
 		// Send to the same people, plus the sender if not ourself
-		to = envelope.to.concat(envelope.from.filter(isNotOwnAddress))
+		to = envelope.to.concat(from.filter(isNotOwnAddress))
 
 		// All CC values are being kept except the replying address
 		cc = envelope.cc.filter(isNotOwnAddress)
 	} else {
 		// Send to the same recipient and the sender (if not ourself) -> answer all
 		to = envelope.to
-		to = to.concat(envelope.from.filter(isNotOwnAddress))
+		to = to.concat(from.filter(isNotOwnAddress))
 
 		// Keep CC values
 		cc = envelope.cc
 	}
 
 	// edge case: pure self-sent email
 	if (to.length === 0) {
-		to = envelope.from
+		to = from
 	}
 
 	return {

src/store/actions.js

@@ -345,7 +345,7 @@ export default {
 					commit('showMessageComposer', {
 						data: {
 							accountId: reply.data.accountId,
-							to: reply.data.from,
+							to: original.replyTo !== undefined ? original.replyTo : reply.data.from,
 							cc: [],
 							subject: buildReplySubject(reply.data.subject),
 							body: data.body,
@@ -360,7 +360,7 @@ export default {
 					const recipients = buildReplyRecipients(reply.data, {
 						email: account.emailAddress,
 						label: account.name,
-					})
+					}, original.replyTo)
 					commit('showMessageComposer', {
 						data: {
 							accountId: reply.data.accountId,