ASG - cannot send mail through smarthost

I had to rebuild an Exchange 2016 server with smarthost set to the US Comodo server:

I’ve sent my destination port from the Exch server to Comodo to use 587 (rebooted). I’ve tried port 25 as well as 465.

Within Exch 2016 I’ve set authentication and TLS. And I’ve tried it without TLS auth - just username and password.

Authentication credentials are same as logging into my Comodo account at: and at

Exch logs report:
2018-03-26T04:43:06.900Z,08D592CC6F0B85F2,SMTP,,-,Messages: 0 Bytes: 0 (Attempting next target)
2018-03-26T04:43:06.901Z,08D592CC6F0B85F3,SMTP,,,Session Failover; previous session id = 08D592CC6F0B85F2; reason = ProtocolError
2018-03-26T04:43:06.901Z,08D592CC6F0B85F3,SMTP,,+,SmartHostConnectorDeliver y 056fc4b2-eb3d-426d-8281-c3f0dad5db41;QueueLength=TQ=2;AN=3;.
2018-03-26T04:43:06.987Z,08D592CC6F0B85F3,SMTP,,>,Established connection to
2018-03-26T04:43:07.765Z,08D592CC6F0B85F3,SMTP,,-,Messages: 0 Bytes: 0 (Attempting next target)
,Session Failover; previous session id = 08D592CC6F0B85F3; reason = ProtocolError
2018-03-26T04:43:07.765Z,08D592CC6F0B85F4,SMTP,,+,SmartHostConnectorDeliver y 056fc4b2-eb3d-426d-8281-c3f0dad5db41;QueueLength=TQ=2;AN=3;.
2018-03-26T04:43:07.853Z,08D592CC6F0B85F4,SMTP,,>,Established connection to
2018-03-26T04:43:08.627Z,08D592CC6F0B85F4,SMTP,,-,Messages: 0 Bytes: 0 (Retry : You have been denied authentication due to possible brute-force attempts;please try again later.)

Comodo tech support has been… slow



Hello @awsic ,

Thank you for your feedback.
Support team already coordinated with you via support ticket regarding this concern.
Please feel free to reply at your convenience.

Thank you.

Thank you, Jay, for the info. I did receive the support email from support. They did offer the right solution: disable authentication in Exchange. I tried that and it resoled my issue.


Hello @awsic ,

It’s good to learn that the resolution we sent worked.
If you have other issues or questions please do not hesitate to reach us through

Thank you.