Delay when forwarding from Exchange to external address

By damista ·
I'm working on a little program to monitor proper operation of a mail server.

An email is sent to an account on the remote server, which points back to an account on the local server. This way, we can tell if the remote server is not only running but also sending and receiving.

Everything works as it should, with the exception that if the remote server is running Exchange, mails are forwarded with a 10 minute delay. First we thought it was a glitch somewhere but when testing with a different Exchange server, the same thing happens.

Mails sent directly from the remote server arrive instantly and other mail servers do not display this behaviour either. Is there a way to turn this delay off? I'm not an expert on Exchange, so I have no clue why this is happening in the first place.


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Some thoughts

by BFilmFan In reply to Delay when forwarding fro ...

If you monitor the queues on the Exchange server, you would be able to tell if it was sending and recieving email without all this email bouncing back and forth. See

Now for your questions:

Has tarpitting been enabled on the Exchange server? This is usually set up to fight spam. See

Otherwise, we need some some information if the email is being sent and recieved via POP, IMPA, or SMTP and their configuration, for example are they configured to use a Reverse DNS lookup before sending mail, do they send directly to the Internet or via another relay like a hardened SMTP gateway appliance.

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by damista In reply to Some thoughts

First of all, thanks for the reply.

Ok, some more info:

We're monitoring the mail servers of several clients for operation. The reason we went with our own little solution is simply because we can tailor it to fit into our infrastructure for client monitoring and we have complete control over the reporting and flagging.

The application sends emails out through SMTP and receives via POP3.

As I mentioned before, Sendmail or Postfix servers forward mails imediately but all Exchange servers return them with a 10 Minute delay.

I have to check with our techos, if the servers have tarpitting enabled. My guess always was that it has something to do with spam control, so this probably is the culprit.

I can live with the way things are but it has its downsides and expands the time frame we'd be able to identify a server that may have a problem.

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