No SMTP sending but, no errors

[Sens0r]

Hello,

I have a strange problem on my standard ispCP RC 6 installation on my debian Server.

In fact, everything concerning the sending/receiving of e-mails works fine, except the sending over smtp from a Mailclient, Thunderbird for example.

First of all, I have to say that the webmail just works perfectly.
The strange "thing" about my smtp Server problem is that I can't get a connection to my server, thunderbird always returns me an error that it didn't managed to connect to the server.

I analyzed several things, I scanned the port range of my server and got the following output (I only pasted the line related to smtp):
25/tcp filtered smtp

which seems to be alright in my eyes, it is filtered to avoid spammers to misuse the server.

Further, I searched the logs of postfix for errors, warnings and so on, but everything is perfect. Then I tried restarting postfix, didn't change anything.

So, again, I have to ask for your help. I would be very pleased if someone could help me.

Thanks a lot & Greetings,
Steven