Hi,
I'm running an IMAP mail server on a root server with Slackware64 14.0, with Postfix and Dovecot. There's no webmail system installed, since all users are expected to use Thunderbird (available for Linux, Windows and Mac OS X).
On most machines, everything runs fine, which means I can configure accounts OK, and users can send and receive mails. Here's how folks are supposed to configure Thunderbird for incoming mail:
- Port: 993
- Security: SSL/TLS
- Authentication: normal password
And for sending mail:
- Port: 25
- Security: STARTTLS
- Authentication: normal password
The server uses a self-signed certificate dovecot.pem.
Curiously enough, on some of the client machines, users can't seem to configure their account. Reception works well, but when they want to send mail, Thunderbird keeps trying to connect to the mail server, in vain.
I don't have the slightest idea why this is so. Now I vaguely wonder if this problem is either related to the firewall or proxy settings.
As far as I understand, the only ports I have to open are 25 and 993 on the server. And that's it. Nothing on the client side. Correct me if I'm wrong.
I'm also using a Squid+SquidGuard proxy on the local server which acts as a gateway. In theory this shouldn't interfere, since only requests to the HTTP port (80) are redirected to port 3128, to be handled by Squid.
Any idea what's going on here?
Niki