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We were using our MDaemon email server on Windows Server 2003 for years without any issue. Since a few days, the IMAP server suddently stop and gave us one error message:

Winsock Error 10013 Permission denied

After a few investigation on Google we found that the port is locked by "something".

So, we changed the classic 143 to a random port (500) and everything worked fine!

After a few tries, we found that telnet xxxxxx 143 give us the answer that the port is OK


So is this message normal or is that an issue?

How is that possible to find the running software that block us to connect to port 143?

Thank a lot for any help.

Kind regards

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up vote 3 down vote accepted

From a command-prompt, execute netstat -a -n -o | find "LISTEN" | find ":143 ". That will return the process identifier (PID) of the program listening on port 143 in the far right column. Open up Task Manager, go to the "Processes" tab, use the "View / Select Columns" menu to add the PID column to the display, then look for the offending process.

Without knowing what the offending process is, though, I can't tell you anything about making it not bind to port 143. Update your question if you need addt'l assistance after locating the process and we can discuss further.

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Seem to be a great asnwer. I voted up and will test, but I think there is 90% probability I will accept, as it seem to answer perfectly! – Waza_Be Sep 19 '11 at 19:03

There is a program called TCPview from Microsoft that can show you which program runs on port 143 (or any other port).

If there is a program listening on port 143 you don't know then you have an issue. But otherwise you should configure this program not to listen on port 143.

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