We still run into problems when changing/saving settings in network config! This morning one employee added a DNS server and saved the changes, and this also made changes to Postfix... it removed the FQDN and added just the hostname breaking the mail traffic. I did realize this when I got back in the office in the afternoon! In other word - Our mail was down all day!
When this happens the mail routs back to it self!
dsn=5.4.6, status=bounced (mail for HOST.DOMAIN.TLD loops back to myself)
And I have addressed this bug/behavior many month ago, with other network issues.
Operating system CentOS 7.7.1908, Webmin version 1.941, Usermin version 1.791, Virtualmin version 6.08 Pro, Authentic theme version 19.45
Best regards, Leffe