Use delivered/envelope/original for identity matching

FAQ.md

@@ -1078,7 +1078,7 @@ 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*, *cc*, *bcc* and *from* addresses will be checked
+For incoming messages the *to*, *cc*, *bcc*, *from* and *(X-)delivered/envelope/original-to* addresses will be checked
 and for outgoing messages (drafts, outbox and sent) the *from* addresses will be checked.
 
 The matched address will be shown as *via* in the addresses section.

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

@@ -103,6 +103,7 @@ import javax.mail.MessagingException;
 import javax.mail.Session;
 import javax.mail.Store;
 import javax.mail.UIDFolder;
+import javax.mail.internet.AddressException;
 import javax.mail.internet.InternetAddress;
 import javax.mail.internet.MimeMessage;
 import javax.mail.search.ComparisonTerm;
@@ -2434,6 +2435,12 @@ class Core {
                 addresses.addAll(Arrays.asList(message.bcc));
             if (message.from != null)
                 addresses.addAll(Arrays.asList(message.from));
+            if (message.deliveredto != null)
+                try {
+                    addresses.add(new InternetAddress(message.deliveredto));
+                } catch (AddressException ex) {
+                    Log.w(ex);
+                }
         }
 
         // Search for matching identity