Some of the outbound emails were bounced back suddenly starting yesterday.
There are three types of undeliverable errors:
1. #552 5.2.0 IB212 msg rejected as spam ##, from secureserver.net
2. #554 5.7.1 [P4] Message blocked due to spam content in the message. ##, from embarq.synacor.com
3. #554 Denied (Mode: normal) ##, from mxlogic.net
I ran a test on mxtoobox.com, and didn't find any error for our domain. It isn't on any blacklist. 4 warnings found:
smtp: mail.domain, SMTP Transaction Time, 8.284 seconds - Not good! on Transaction Time
smtp: mail.domain, SMTP TLS, Warning - Does not support TLS.
dns: domain, DNS SOA Expire Value, SOA Expire Value out of recommended range
dns: domain, DNS SOA Serial Number Format, SOA Serial Number Format is Invalid
What's causing the problem? Can anyone help please?