Mail delivery problem

[pluckyduck]

Hi all,

we are trying to send mail to a domain xyz.de.
This domain has three mailservers.
iron1, iron2 and charion. iron1 and iron2 do not respond, they are probably down. We don't know. We get informed about this by the following message:

host iron2.xyz.de[1.2.3.4] refused to talk to me: 421 4.4.1 myserver.mydomain.de Unable to contact destination.

The same message is send back to us a few days later regarding host iron1.

So heres the question:
In which (time related!) order does the proxmox gateway tries to contact the different servers? In other words: It should contact the servers in the order of their mx priority, but what time-lacks occur between the diffent tries, and how can the be modified?
It seems to me as if the server was not able to deliver the mail through the charion-host up to now (more than 5 days have passed) and is still trying iron1 and/or iron2.

Do you have any hints or solutions?

Thanks in advance
Steven

 

[dietmar]

The SMTP client looks up a list of mail exchanger addresses for the destination host, sorts the list by preference, and connects to each listed address until it finds a server that responds.

When a server is not reachable, or when mail delivery fails due to a recoverable error condition, the SMTP client will try to deliver the mail to an alternate host.

If delivery fails it informs the queue manager that delivery should be tried again at a later time. We use Postfix as mail transport agent, so you can find details there:

http://www.postfix.org/QSHAPE_README.html#deferred_queue

We use resonable settings for all timing:

maximal_queue_lifetime (5 days): The maximal time a message is queued before it is sent back as undeliverable.

delay_warning_time (default: 4 hours): The time after which the sender receives the message headers of mail that is still queued. Configurable on the web interface (Mail Proxy/Limits)

Best Regards,

Dietmar

 

[ofanz]

> Do you have any hints or solutions?

Tell them to bye more reliable Mail Servers ;-) A mail server schould not be down for such a long time (5 days). Especially because there are easy ways to avoid it (Backup MX Records).

- Otto

 

[martin]

hi,
it looks like that the server iron2 are online and responding, but refused to talk. if a server is responding, no other smtp server will be contacted. only if the iron2 is not responding (offline), then other smtp server will be contacted.

iron1 is contacted, because the MX record has the same priority.

server charion is never contacted, because iron1 or iron2 are online.

this behavior is RFC compliant (http://www.faqs.org/rfcs/rfc2821.html)

solution: on your side, you can do nothing. its no good idea to run not working mail servers - so please inform the addressee, he should take the non working smtp server offline.

regards,
martin