I have had some user complaints about email being delayed after doing
some investigation I found out that sure enough it was happening.
About one in 20 was getting delayed about 20 - 30 minutes during this
time other emails could skip over it, but one email would get hung.

Basically what I did was email

To: user2@external.com
CC: user4@internal.com
From: user3@internal.com
Subject: Testing #<number>
This is test #<number>

When I went through this I found that messages from 1-4 went through
fine. Then message 6 - 11. Message 5 took 20 minutes to arrive. I
checked at my firewall and this is the order that they appeared there.
So it appears to be definitely something in postfix that is causing the
problem.

I need any help I can get in how to trouble shoot this. If I do this
again, how do I find the mail, where is it hanging.