sendmail relay error after exchange 2003 upgrade

[CyberNerd]

recent upgrade to MS exchange 2003

since then sendmail relay is displaying

       (I/O error: Input/output error)

in mailq and /var/log/maillog to addresses on the new exchange server.
it seems to be fairly random - about 3-4 per day but never to any servers other than the exchange. most mail gets through.
I get a constant ping to exchange server, IMHO network is good.
not fscked the mail relay (do I need to?) I'm thinking problem with exchange but can't find any pointers.
sendmail is sendmail-8.12.8-9.90

Any ideas

[Alex]

checked the smtp service / settings / logs on the exchange box.

[Roberto]

Isn't that error related to internal file I/O in sendmail, rather than to network transmit/receive?

[Geoff]

Yes, that's correct Roberto. Basically it can't connect to the exchange box. It's only a temporary error though, it'll retry later. One thing I would check is if rDNS records for exchange are correct. Sendmail is very fussy about that. Failing that, break out your network monitoring tools. Nagios, Cacti, etc.

[CyberNerd]

Thanks, this *seems* to be working now.
There was an historic firewall rule in the relay preventing communication with one of the AD DNS servers, I guess it occasionally didn't get the PTR for the new exchange.

[Geoff]

i know this isn't the question you asked, but have you considered 'upgrading' sendmail to a less brain damaged MTA like postfix or Exim?

[CyberNerd]

yep, its at the bottom of the list of things to do.
personally I'm happier with postfix, but in general the sendmail box is too reliable to 'fix' atm

[Geoff]

If it ain't broke, etc?