This is a known concern for SDM 17.1.
From the log entries, the key is this item:
2018-01-30 17:04:21:432 ERROR [mailNxdActorSystem-akka.actor.default-dispatcher-8] c.c.S.m.NXJavaMailMailer - The transport is not connected or is dead.
javax.mail.AuthenticationFailedException: No authentication mechanisms supported by both server and client
At the Mail server end, NTLM would have been configured as a preferred connection mechanism from JAVA clients such as the maileater. The Mailer java code will try to send user name and password when attempting to connect. Since the 2 configurations (plain vs NTLM) don't match, the given error is presented.
At the present, the workaround is to uninstall the options username and password and even the domain.