Hi,
on a version 9 Sophos UTM120 physical appliance, I have configured NAT rules for inward POP3 and SMTP traffic.
While receiving emails works flawlessly, and sending emails by POP3-clients as well, as long as they access the mail-server by its internal IP-address, the problems start when clients try to send emails from external addresses, thus connecting through the firewall.
POP3-clients receive an error message, that states that the SMTP-authenticiation is malconfigured (SMTP error-code: 501)
For POP3- and SMTP-protocol as well as any traffic from and to the mail servber, exceptiond have been configured in IPS and web protection.
Network protection livelog shows a successful POP3 SYN, when clients try to access the server.
Could anybody give me ahint, where to start lokking for answer concerning this issue.
I am convinced, that it is a problem caused by the Sophos UTM, since it never occured when the old LanCOM-firewall, that the Sophos UTM replaceed, was in use.
Best regards
Tobias
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