Lately I noticed some slowness with my SMTP service. When I tried to do a
telnet session, I noticed that it was slow in doing the RCPT TO
validation/resolving. Have any one experience this problem? Any solution to
this?

Thank you
Lucas

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Are you using Exchange for recipient validation (note that there are
several other methods, and you didn't specify)? Has the response time
of your Exchange server in general increased? If you are referring
specifically to slow _failed_ lookups, do you have tarpitting enabled,
which is designed to do just that?

I use Exchange for recepient validation. In the beginning it seemed that it
is ok in term of speed, but its getting slower in general. Also I just
checked and we don't have the tarpitting on (by looking at the registry
setting).

Lucas

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*How* slow? If the RCPT TO response the only part of the conversation
that's slow, and it's < 10s, you're fine as far as even the strictest
remote server will judge.

The response time is linked to the speed of your Exchange SA, and in
turn to the response time of your GCs. Is it possible that some part
of your AD infrastructure has become unresponsive without you knowing
it, and requests are being steered to an offsite and/or slower GC? Do
you benchmark Exchange response time, so you can see if there has been
appreciable slowdown in the services in general over time? If the SA
is struggling, that won't be noticeable moment-to-moment in Outlook,
but only when specific functions are invoked.