I've set up a mail server on Ubuntu 12-04 following the server guide using Postfix and Mail-Stack Delivery instructions.
My server has it's FQDN and a fixed IP address and is alone in it's network. My users however are all remote connecting from different networks (homes, hotels,...).
We use the imaps protocol to read our mail and it works perfect with Thunderbird and Mac Mail on port 993. However I can't get the server to accept connections on the SMTP ports 25 or 587 when I want to send mail.
When I run
nmap localhost I see that 25/tcp is open but not 587. When I force Thunderbird to use port 25 with SSL I get a time-out.