What's the likely culprit in email delay?

Question

If anyone can shed light or point me to a tutorial, I'd appreciate it. We are a tiny company and have experienced occasional delays in receiving email sent between staff members. We are in separate cities but all in the same state; our webhost/email ISP is across the country from us. If it matters, we're on Macs and most of use Entourage. Our email configurations are POP server: companyname.com and SMTP: smtp.companyname.com (When we used our DSL providers for SMTP we had unreliable service) Our ISP says they're not seeing delays related to their equipment and the problem is elsewhere in the network. A co-worker believes that the delays are with the ISP. Is there a good way to figure this out?

Answer 1

Take a look at the headers of the email. You'll see lines that start with Received: which indicate the path the e-mail took (read them from bottom to top). They should also have a time stamp which will let you know if there's any delay in the mail server system(s).

For example, you might find lines like:

Received: from server1.example.com ([1.2.3.4])
    by server2.example.com (Postfix) with ESMTP id 93F1F5001BE
    for <employee@example.com>; Fri, 19 Mar 2010 02:05:07 +0000 (UTC)

Received: from sender-pc.example.com ([1.2.3.2])
    by server1.example.com (Courier) with ESMTP id 9AF35001BDF
    for <employee@example.com>; Fri, 19 Mar 2010 02:04:52 +0000 (UTC)

Notice in my example that the timestamps are only 15 seconds apart, this would be fairly normal (though times up to a couple minutes would also be normal).
Also note, there may be other stuff in between some of the Received lines, they don't have to be grouped together.

Answer 2

@Chris S has it right for troubleshooting, but what sort of delays are you experiencing? SMTP/POP is not a "push" email service like Microsoft Exchange is.