I am hoping someone has had a similar situation or a place to point me as I'm at my wits end and have users unable to send emails.
I've had a toaster running for several years. This particular system has been running without issues for roughly 12 months after migrating from CentOS 6 to CentOS 7. I didn't make any changes yesterday, and email was flowing perfectly. This morning, we aren't able to authenticate, with Outlook reporting 'None of the authentication methods supported by this client are supported by your server'. Multiple Android clients are reporting similar errors. The firewall in front of the server and iptables have 587 open (again, no changes intentionally made in the environment). I can connect with openssl s_client -starttls smtp -crlf -connect <server>:587. What is missing is the AUTH line and if I try to execute an AUTH, I get 503 auth not available (#5.5.3). Selinux is disabled. My /var/log/maillog stops reporting any vchkpw-submission activity around 0600 this morning. I've searched and not seen where vchkpw just stops doing anything. I'm investigating whether the server has been compromised, but nothing is showing so far, and this is a very odd behavior to execute if it were. Any thoughts? My users have been down since this morning, and I'm flummoxed. Thank you! Chas