No SMTP server defined. Use real server address instead of 127.0.0.1 in your account

Solution 1:

If you use avast on your server, you need to disable the Spam Shield and Mail Shield components on your server. Apparently they are for workstation use only. You can leave the "Exchange" Shield on to keep protecting your email server.

Source: https://forum.avast.com/index.php?topic=228734.0

Re: Avast Business Antivirus - block e-mail from my server to gmail

Quote from: kel2 on September 03, 2019, 04:12:23 PM

Found this ... Why has it been working for so long and now stopped ... https://kb.support.business.avast.com/GetPublicArticle?title=No-SMTP-Server-Defined-Error-BAV#

I'm unsure how to answer your question, but like the Avast Firewall, both the Mail Shield and the Anti-spam components are designed only for workstations and not mail servers. I've heard our development/production team are working on a permanent solution that will automatically remove these components if the Avast installation detects Exchange on the server.