External Mail Routing

[k3lvin]

Things have been running pretty smoothly on our Domino sever for some time but recently some things I dont understand are happening. Mail to certain domains will not route, which I know I use to be able to send mail to just last week. About 95% if of all our mail gets routed fine but some of our mail will just not route, it will just sit in the mail.box's and say 'pending' then eventualy send a delivery failure report back to the sender.

Example taken from Server Console:

'Router: Failed to connect to SMTP host ALEXANDRABROAD.CO.UK because The server is not responding. The server may be down or you may be experiencing network problems. Contact your system administrator if this problem persists.'

Ive done a nslookup for ALEXANDRABROAD.CO.UK and its mx record is ibmr.btconnect.com which I can telnet into from our mail server so there are no connectivity problems.

Im not sure where to go from here, any help would be great. Thanks

Windows Server 2003 SP1
Domino 6.5

 

[m4ilm4n]

When you telnetted to the destination host, was that to port 25 of alexandra (just to make sure resolution of the MX is working).

If so, how long did the destination host take to respond to a HELO or EHLO command?

 

[k3lvin]

Hey thanks for the response.

Yeah I telnetted using port 25 successful. How do I do a HELO or EHLO command?

 

[m4ilm4n]

They're basic SMTP commands. Here's a good example of an entire command sequence:

http://www.yuki-onna.co.uk/email/smtp.html

What you're trying to do is manually execute the commands the mail server would normally do. Remember that the sequence of commands is important, e.g. the "MAIL From:" must come before the "RCPT To:".

You should get responses from the destination server that will give you a clue about what's going on.

 

[k3lvin]

I'm 99% sure the problem is to do with our Fully qualified Internet host name. (Server Document, Basics tab) Previously we had something in there that did not exist at all! (according to a DNS checker) so I used our vpn.companyhostnamehere.co.uk host name which a DNS checker recognizes as a valid domain name. Since using this name some mail which was not being able to be sent is now sending but still not all. I wonder if we need to register a new host name for mail purposes only such as mail.companyhostnamehere.co.uk?

Any thoughts?

 

[m4ilm4n]

That'll definitely break it - the FQDN of the Domino server has to be resolvable and reachable on port 25 from the outside world for SMTP mail to flow, otherwise a receiving MTA that performs reverse lookups as an anti-spam tool (a very common technique) will fail the connection.