Debian Etch | no connection via IMAP

Today i found out that on one of my servers, i can not establish a connection via IMAP.

The portscanner within the ISPConfig (on the server itself), shows that the following IMAP ports are open:

Port 143 (tcp) is open (imap2)!
Port 993 (tcp) is open (imaps)!

netstat -tap | grep imap shows me:
tcp6 0 0 *:imaps *:* LISTEN 1980/couriertcpd
tcp6 0 0 *:imap2 *:* LISTEN 1968/couriertcpd

But when i try to establish a connection via telnet from my local desktop with:
telnet 12.34.56.789 143

It fails...

The firewall on port 143 within ISPConfig is disabled.

Within Outlook Express i receive the error code: 800ccc0e
This means that a connection is not possible.

My conclusion is that i can not establish a connection via port 143 from outsite the mailserver.

Any suggestions to solve this problem?

 

For me the cause of this temporary problem, is unknown, but i solved it by restarting the firewall on that mailserver within ISPConfig.
Everything is fine again!