ESMTP not working in cisco 3900 router

[murugananthama]

Dear Friends,

I have cisco 3900 router and connected with MPLS link for intranet access.

ESMTP mail server has been deployed in the data center and  firewall inside  IP is  configured as default gateway in the server.

I am using IMAP ( port 993)  protocol for incoming and esmtp ( port 25)  for outgoing mail.   Outlook mail clients are unable to receive mails  ( MPLS link is connected between data center and brach) . whenever packets crossing the router, the mail flow is stopped working.

I have tried to telnet the esmtp port 25 from the router with the source ip of  LAN interface IP. it is throwing the following response.

220 ********************************\r\n

I have captured the response in wireshark and below are the output. its just printing astrisk ( output trimmed)

Transmission Control Protocol, Src Port: 25 (25), Dst Port: 50086 (50086), Seq: 1, Ack: 1, Len: 38
Simple Mail Transfer Protocol
Response: 220 ********************************\r\n
Response code: <domain> Service ready (220)
Response parameter: ********************************

If packet is not crossing the router, then its working fine ( connected laptop in the core switch and accessed the mail & its working).

see the below response in the wireshark capture.

Simple Mail Transfer Protocol
Response: 220 smtp.mycom.co.in ESMTP Postfix\r\n
Response code: <domain> Service ready (220)
Response parameter: smtp.mycom.co.in ESMTP Postfix

How to fix this issue ?? Kindly help me ..... Thanks in advance .....

Regards,

Murugan.

[Mark Malone]

Have you checked with the provider of the mpls link that there PE router is not blocking the port no for ESMTP , by default routers are fully open so if you have not blocked it on your end theres a possibility there filtering on the PE where the mpls termites at ISP side ? Its strange though they would block such a standard known port

If you bypass your firewall does it work could be blocked there also ?

[murugananthama]

Hi Mark, 

While trying telnet from router with source of LAN interface IP, we are getting the  below response.

220 ********************************\r\n

that means, there is some issue in the router itself. it seems that router is unable to accept the server's response. 

the same issue can be fixed in asa or pix by using the below command 

no fixup protocol smtp 25  ( disabling mail guard inspection)

But I have Cisco router 3925 in my environment.  so problem is obvious here but no idea how to fix this problem in  the router. any help will be appreciated... Thanks in advance ...!!

Regards,

Murugan.