Cisco 871 SMTP not working after firewall is enabled

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Jul 23rd, 2008
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I have a Cisco 871, everything is owrking fine is firewall is disable, but when I enable it allowing HTTP, HTTPS, DNS, POP3 and SMTP (ANY<->ANY)I can only send emails to users in the same domain of the sender for the rest I receive "550 5.7.1 Unable to relay for [email protected]".

I changed the SMTP port in the Exchange side from 25 to 26 and I enableled the por 26 in the firewall and evething works fine.

Does Cisco IOS has a special configurationfor port 25 that I need to check?


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tstanik Tue, 07/29/2008 - 14:24
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No, Cisco IOS has no any a special configuration for port 25. When POP3 clients send messages, the Exchange Server computer is communicating with an SMTP (Simple Mail Transfer Protocol) host. This requires access to TCP port 25. The Internet Mail Connector and the Internet Mail Service use TCP port 25 for inbound SMTP messages as defined by RFC-821. For inbound SMTP messages, the Internet Mail Connector and Internet Mail Service monitor port 25 for incoming connections from other SMTP hosts. Microsoft Exchange Server supports POP3 as defined in the RFC- 1734 and RFC- 1957 specifications.


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