Use delivered to header for identity matching

FAQ.md

@@ -704,7 +704,7 @@ Note that this is independent of receiving messages.
 **(34) How are identities matched?**
 
 Identities are as expected matched by account.
-For incoming messages the *to* and *cc* address will be checked and for outgoing messages the *from* addresses will be checked.
+For incoming messages the (delivered) *to* and *cc* address will be checked and for outgoing messages the *from* addresses will be checked.
 Archived messages will be considered as incoming messages, but additionally the *from* address will be checked.
 
 The matched address will be shown as *via* in the addresses section.

app/src/main/java/eu/faircode/email/Core.java

@@ -75,6 +75,7 @@ import javax.mail.Session;
 import javax.mail.Store;
 import javax.mail.StoreClosedException;
 import javax.mail.UIDFolder;
+import javax.mail.internet.AddressException;
 import javax.mail.internet.InternetAddress;
 import javax.mail.internet.MimeMessage;
 import javax.mail.search.ComparisonTerm;
@@ -1143,6 +1144,7 @@ class Core {
             }
 
             if (message == null) {
+                String deliveredto = helper.getDeliveredTo();
                 Address[] froms = helper.getFrom();
                 Address[] tos = helper.getTo();
                 Address[] ccs = helper.getCc();
@@ -1153,6 +1155,13 @@ class Core {
                     if (froms != null)
                         addresses.addAll(Arrays.asList(froms));
                 } else {
+                    if (deliveredto != null)
+                        try {
+                            for (Address address : InternetAddress.parse(deliveredto))
+                                addresses.add(address);
+                        } catch (AddressException ex) {
+                            Log.w(ex);
+                        }
                     if (tos != null)
                         addresses.addAll(Arrays.asList(tos));
                     if (ccs != null)
@@ -1195,7 +1204,7 @@ class Core {
                 message.references = TextUtils.join(" ", helper.getReferences());
                 message.inreplyto = helper.getInReplyTo();
                 // Local address contains control or whitespace in string ``mailing list someone@example.org''
-                message.deliveredto = helper.getDeliveredTo();
+                message.deliveredto = deliveredto;
                 message.thread = helper.getThreadId(context, account.id, uid);
                 message.receipt_request = helper.getReceiptRequested();
                 message.receipt_to = helper.getReceiptTo();

app/src/main/java/eu/faircode/email/MessageHelper.java

@@ -449,7 +449,10 @@ public class MessageHelper {
     }
 
     String getDeliveredTo() throws MessagingException {
-        return imessage.getHeader("Delivered-To", imessage.getHeader("X-Delivered-To", null));
+        String header = imessage.getHeader("Delivered-To", null);
+        if (header == null)
+            header = imessage.getHeader("X-Delivered-To", null);
+        return header;
     }
 
     String getInReplyTo() throws MessagingException {