do not forward to unverified mailbox

email_handler.py

@@ -482,6 +482,10 @@ async def handle_forward(
     # no need to create a copy of message
     if len(mailboxes) == 1:
         mailbox = mailboxes[0]
+        if not mailbox.verified:
+            LOG.debug("Mailbox %s unverified, do not forward", mailbox)
+            return [(False, "550 SL E18 unverified mailbox")]
+        else:
             ret.append(
                 await forward_email_to_mailbox(
                     alias, msg, email_log, contact, envelope, smtp, mailbox, user
@@ -490,9 +494,20 @@ async def handle_forward(
     # create a copy of message for each forward
     else:
         for mailbox in mailboxes:
+            if not mailbox.verified:
+                LOG.debug("Mailbox %s unverified, do not forward", mailbox)
+                ret.append((False, "550 SL E19 unverified mailbox"))
+            else:
                 ret.append(
                     await forward_email_to_mailbox(
-                    alias, copy(msg), email_log, contact, envelope, smtp, mailbox, user
+                        alias,
+                        copy(msg),
+                        email_log,
+                        contact,
+                        envelope,
+                        smtp,
+                        mailbox,
+                        user,
                     )
                 )