sendmail: Time Out

Hello, experts!

Recently, I recv'd some complaints from various user of mine that some of there senders cannot send an e-mail to our site.  What is confusing, is that I would say that 5% of senders can't.  Went to and checked my e-mail and got the result below: -  [Could not connect: Could not receive data: Operation timed out.]
  [Note that if your mailserver takes over 30 seconds to respond, our test will timeout, even though real mailservers will wait longer]

Ran ethereal on my desktop and ran telnet on my e-mail box and discoverred that it does take 40.189 sec for SMTP to begin.  Time was after the handshake frame to when SMTP kicked in.  Checked another e-mail server and it was way slower.  I am running sendmail with the latest patch from RedHat.  Does anybody have any clue as to what is going on?  

As always, thank you!  In advance for your time on this matter.
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0) Check timeout Timeout.ident in your
It specifies how long sendmail is supposed to wait for ident query reply.
In older releases it has been RFC recomended 30s in newer releases it is 5s.
Quite a few people recomend turning it off by setting timeout to 0.

1) How many RBLs do you use? [Which ones?]
[ an unresponsive RBL may cause similar effects ]

2) Check that all DNS servers specified in /etc/resolv.conf are up and running.
Unresponsive first DNS server may cause extra 5s delay per every DNS query.
[ reverse DNS (ip->name->ip); RBL checks ]

3) Does the "problematic" host have properly configured reverse DNS?
PTR record to map IP to name and A record to map name to the IP
BinaryJobAuthor Commented:

Thanks for the advise.  Will check recommendation and will get back to you.  Again, thank you!
BinaryJobAuthor Commented:

It was one of the RBL's!  I temporarily removed all of them and sure enough, mail got through.  Question, I have a few of them that I use, how can I test to make sure that they are working?  Better yet, which is failing?

Thank you!
Write a simple test script (e.g. in perl) to monitor responce times of RBLs you use.

For medium minus mail sites one check per day and manual sendmail reconfiguration in case of problems should be sufficient (IMHO).
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