There are many reasons this can happen:
- the domain is allowed to override SMTP authentication
- the IP ADDRESS of the domain is set for SMTP authentication bypass
- an external server is accepting e-mail for your server and forwarding to the domain, without being required to authenticate or is listed in SMTP authentication bypass.
If they are not already set to detailed, set your SMTP LOGS to DETAILED and then check to see what is shown for anyone sending to the domain.
If the issue happens with a specific sender, then search for that sender.
Phonr: (773) 491-9019
Phone: (224) 444-0169
E-Mail and DNS Security Specialist
Network Security Specialist
Customer Service Portal: https://portal.chicagonettech.com
Security Blog: http://networkbastion.blogspot.com/
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