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From: RICCARDO on 2 Aug 2010 12:14
My mail server is getting this error to send messages to specific
domain "X".
I verified there are 6 MX records for this X domain and in my maillog
I can see thiese errors:

SYSERR(root): timeout writing message to mx1.domain.com: Resource
temporarily unavailable
SYSERR(root): timeout writing message to mx2.domain.com: Resource
temporarily unavailable
SYSERR(root): timeout writing message to mx3.domain.com: Resource
temporarily unavailable
....
SYSERR(root): timeout writing message to mx6.domain.com: Resource
temporarily unavailable

Initially I thought to my dns but i resolves names correclty, I ask to
mydomain.com admin and He answered me nothing has been modified.
I tried to use telnet direclty on mx1.domain.com and mx5.domain.com
and I sent emails correctly.
I noted in mailog that sendmail tries to send msg every 5 minutes.
In a week I noted 420 msg with this error where 403 are about
domain.com

What can you suggest me to verify ?

From: ska on 3 Aug 2010 04:03
RICCARDO wrote:
> Initially I thought to my dns but i resolves names correclty, I ask to
> mydomain.com admin and He answered me nothing has been modified.
> I tried to use telnet direclty on mx1.domain.com and mx5.domain.com
> and I sent emails correctly.

So, msg per telnet works.

> I noted in mailog that sendmail tries to send msg every 5 minutes.
> In a week I noted 420 msg with this error where 403 are about
> domain.com

Do all msgs to domain.com tempfail? Maybe, one particular message gets
blocked, e.g. because of certain content, and a firewall in-between
simply cuts the connections? E.g. simply discards all packets so the
TCP connections is not finished in a good way.

> What can you suggest me to verify ?

force one message to the domain from the queue. If it fails, retry
with telnet immediately (from the same host), so you check the
firewall problem. If it succeeds, retry next message, so you check a
problematic msg.

sniff the connections to the MXs when you force one message from the
queue. If you can, sniff on your outer most firewall. So can get an
idea, which side sent the last packet and what kind of packet.

Regards, ska
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