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SMTP conversation interupted

Level 1
Level 1

We receive our mail through our ISP. However some of the mail is stuck in their queue with the following error message "status=deferred (conversation with x.x.x.x timed out while sending RCPT TO. this is only for some users though and not all. I have used a network monitor software and our server responds to the RCPT TO with 250 2.1.5 | 354 Start mail input; end with . and sends a retransmission after getting no response from the sending server.

We have no anti spam software installed on the server.

We have a Cisco 800 series router. How can I find out why the router is not passing on that particular command. We have NAT enabled on the router. On the internal interface I have noticed that the command "250 2.1.5 | 354 Start mail input; end with " is transmitted to the external interface.

We do not have any rules enabled on the router, no firewall and no PIX. How is it possible to tell at what point the command fails and why it fails?

1 Reply 1

Level 9
Level 9

There might be a problem with the mtu size on your wan link.

Perhaps you are using pppoe or similar?

In this case your mtu is less than 1500 and you need to set the ip tcp mss accordingly.

Please check cisco document id 25885.



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