The Case of the Mysterious Mail Delay

I spent the afternoon trying to diagnose some email problems on a client’s LAN. They have a mixed environment of Windows and Unix servers. Their internal DNS server is a Windows 2000 box. Their external DNS server and email server are Red Hat Linux boxes. Sometime yesterday, for no apparent reason they began experiencing a 30-45 second connection delay between the email server and their email clients (mostly MS Outlook – yes, I’ve warned them that Outlook is the single biggest propagator of viruses in the known Universe but they still use it).

We checked all the usual suspects. No DNS problems, no recent changes to BIND or, no sign of DoS attacks, rootkits, viruses, etc. I’ve seen a similar problem caused when the Timeout.ident value in Sendmail is set too high but this was not the problem either. For now, it’s a mystery but further experiments will hopefully turn up the cause.