Send DSN to return path address

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

@@ -2148,6 +2148,7 @@ class Core {
                         message.dkim = MessageHelper.getAuthentication("dkim", authentication);
                         message.spf = MessageHelper.getAuthentication("spf", authentication);
                         message.dmarc = MessageHelper.getAuthentication("dmarc", authentication);
+                        message.return_path = helper.getReturnPath();
                         message.submitter = helper.getSender();
                         message.from = helper.getFrom();
                         message.to = helper.getTo();
@@ -2846,6 +2847,7 @@ class Core {
             message.dkim = MessageHelper.getAuthentication("dkim", authentication);
             message.spf = MessageHelper.getAuthentication("spf", authentication);
             message.dmarc = MessageHelper.getAuthentication("dmarc", authentication);
+            message.return_path = helper.getReturnPath();
             message.submitter = helper.getSender();
             message.from = helper.getFrom();
             message.to = helper.getTo();

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

@@ -64,7 +64,7 @@ import static eu.faircode.email.ServiceAuthenticator.AUTH_TYPE_PASSWORD;
 // https://developer.android.com/topic/libraries/architecture/room.html
 
 @Database(
-        version = 185,
+        version = 186,
         entities = {
                 EntityIdentity.class,
                 EntityAccount.class,
@@ -1816,6 +1816,13 @@ public abstract class DB extends RoomDatabase {
                         Log.i("DB migration from version " + startVersion + " to " + endVersion);
                         db.execSQL("ALTER TABLE `message` ADD COLUMN `notes` TEXT");
                     }
+                })
+                .addMigrations(new Migration(185, 186) {
+                    @Override
+                    public void migrate(@NonNull SupportSQLiteDatabase db) {
+                        Log.i("DB migration from version " + startVersion + " to " + endVersion);
+                        db.execSQL("ALTER TABLE `message` ADD COLUMN `return_path` TEXT");
+                    }
                 });
     }
 

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

@@ -148,6 +148,7 @@ public class EntityMessage implements Serializable {
     public Boolean reply_domain; // differs from 'from'
     public String avatar; // lookup URI from sender
     public String sender; // sort key: from email address
+    public Address[] return_path;
     public Address[] submitter; // sent on behalf of
     public Address[] from;
     public Address[] to;

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

@@ -3619,9 +3619,12 @@ public class FragmentCompose extends FragmentBase {
 
                             if ("list".equals(action) && ref.list_post != null)
                                 data.draft.to = ref.list_post;
-                            else if ("dsn".equals(action) && ref.receipt_to != null)
+                            else if ("dsn".equals(action)) {
-                                data.draft.to = ref.receipt_to;
+                                if (EntityMessage.DSN_RECEIPT.equals(dsn) && ref.receipt_to != null)
-                            else {
+                                    data.draft.to = ref.receipt_to;
+                                else if (EntityMessage.DSN_USER_UNKNOWN.equals(dsn) && ref.return_path != null)
+                                    data.draft.to = ref.return_path;
+                            } else {
                                 // Prevent replying to self
                                 if (ref.replySelf(data.identities, ref.account)) {
                                     data.draft.from = ref.from;

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

@@ -2431,7 +2431,8 @@ public class FragmentMessages extends FragmentBase implements SharedPreferences.
                 popupMenu.getMenu().findItem(R.id.menu_reply_to_all).setVisible(recipients.length > 0);
                 popupMenu.getMenu().findItem(R.id.menu_reply_list).setVisible(message.list_post != null);
                 popupMenu.getMenu().findItem(R.id.menu_reply_receipt).setVisible(message.receipt_to != null);
-                popupMenu.getMenu().findItem(R.id.menu_reply_user_unknown).setVisible(experiments);
+                popupMenu.getMenu().findItem(R.id.menu_reply_user_unknown)
+                        .setVisible(experiments && message.return_path != null && message.return_path.length > 0);
                 popupMenu.getMenu().findItem(R.id.menu_new_message).setVisible(to != null && to.length > 0);
                 popupMenu.getMenu().findItem(R.id.menu_reply_answer).setVisible(answers != 0 || !ActivityBilling.isPro(context));
 

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

@@ -1239,6 +1239,10 @@ public class MessageHelper {
         return addresses;
     }
 
+    Address[] getReturnPath() throws MessagingException {
+        return getAddressHeader("Return-Path");
+    }
+
     Address[] getSender() throws MessagingException {
         return getAddressHeader("Sender");
     }