Overview

If email is not sent by Layton ServiceDesk, despite the test successfully sending an email, this error may appear in the log:

   SmtpException. Failed to send out mail, Id:2059. Detail:Mailbox unavailable. The server response was: 5.7.1 Unable to relay

Fix

Go to Administration > System Settings > Email Server Settings.
Enter the port 587 (or alternative, if configured that way on your mail server).
Check SSL/TLS.
Click the Save button .
Test settings.