I have searched on the internet for a solution for my problem and I'm sure for also a lot of other people but I can't find the answer.
I have installed Thunderbird on my Windows7 professional laptop and I can receive all my mails but I can't send emails out.
On my server I have Ubuntu with postfix installed which works perfect with all other computers in my network with Windows XP together with Thunderbird.
Then I have searched and read a lot of same problems, so the issue is Windows7 which won't let Thunderbird go through their OS because when I tried Microsoft Outlook with imap this worked fine.
I already have disabled the FW in Win7 and added a new rule for port 25 but without success.
Maybe someone here on board has a solution for this? Or am I forced now to use another email program?

do we get to see your logs? or, do we have to guess?

Ofcourse you may see my logs, I have no secrets but what log do you need? the one from /var/log/mail.log ? because ther you can't see anything cause TB doesn't even get there to my server.

Ryan

maybe so, but it doesn't hurt to check the logs for confirmation. you can look for postfix logs
of connection attempts. they should be in lines containing "postfix/smtpd", i think.

edit: on the windows side (which i don't know very much about), if you can't
connect after turning off the virus scanner (which can prevent
TLS connection), you can diagnose the problem by looking at a wireshark capture.

In the mail.log there are a lot of imapd login connectons which works ok from win xp machines.

Strange thing, I also installed PegasusMail and with this program I can send through smtp port 25 to my imapd even without authentication.

I'm also busy with wireshark...

Moved: This thread is more suitable in General and has been moved accordingly to help your thread/question get the exposure it deserves.

What the error (on TB) exactly says ?

Problem solved, the issue was in McAfee Epolicy Orchestrator.
There is a rule in it called "anti virus standard protection" rule section
and the rule you want to switch blocking off for is called "Prevent mass mailing worms from sending mail"

This one was blocking Thunderbird sending outgoing mails on Win7 systems.
The same policy is used on WinXP machines (where TB still works fine) but somehow there has to be a different kind of interpretation in both systems for this rule.

Adter long searching and testing I have found the problem.

very good, rytec. thank you for posting back with the solution.