The system is hosted Ubuntu 18.04 on UpCloud public IP. I build the system using the excellent and easy instructions here: http://nerdvittles.com/?p=25930. I have also enabled no-authentication SMTP Relay on port 25 with the IP of my server AND whitelisted the IP for incoming mail. The only thing I can guess is that Google is rejecting the message because the mail is coming from pbx1.mydomain.com and I have no "pbx1" user? Here are the logs: Code: Sep 18 12:11:05 pbx1 sm-mta: starting daemon (8.15.2): [email protected]:10:00 Sep 18 12:57:00 pbx1 sendmail: x8ICv0o5006165: from=asterisk, size=25400, class=0, nrcpts=1, msgid=<[email protected]>, [email protected] Sep 18 12:57:00 pbx1 sm-mta: x8ICv0jC006166: from=<[email protected]>, size=25533, class=0, nrcpts=1, msgid=<[email protected]>, proto=ESMTP, daemon=MTA-v4, relay=pbx1.mydomain.com [127.0.0.1] Sep 18 12:57:00 pbx1 sendmail: x8ICv0o5006165: to="John Borhek" <[email protected]>, ctladdr=asterisk (1000/1000), delay=00:00:00, xdelay=00:00:00, mailer=relay, pri=55400, relay=[127.0.0.1] [127.0.0.1], dsn=2.0.0, stat=Sent (x8ICv0jC006166 Message accepted for delivery) Sep 18 13:07:01 pbx1 sm-mta: x8ICv0jC006166: to=<[email protected]>, ctladdr=<[email protected]> (1000/1000), delay=00:10:01, xdelay=00:10:01, mailer=esmtp, pri=145533, relay=alt3.aspmx.l.google.com. [188.8.131.52], dsn=4.0.0, stat=Deferred: Connection timed out with alt3.aspmx.l.google.com. THX!