I have hMailServer installed on Windows Server 2008. It's all set up and working, except that I can't send mail from it through Thunderbird (getting an SMTP timeout message) from my own PC (which is not in local network with the server). I have checked the settings multiple times, and they are correct. With a non-standard port (as in, not 25), I could send mail, but due to it being non-standard, those mails never got to the recipients.
Telnetting to the server through port 25 works. The ports are open from the firewall. Sending mail "locally" from the server works (and auto-reply works). My Thunderbird settings let me authenticate and send mail when the SMTP server is using a non-default port, but not when it's using 25, the default port. I can access other SMTP servers all fine through 25, and disabling my own firewall didn't help.
The exact error message is this (mind the Finnish at the start):
Postia lähetettäessä tapahtui virhe: postipalvelimen kättelyviesti oli virheellinen: Cannot connect to SMTP server 18.104.22.168 (22.214.171.124:25), connect timeout
Repeating, I can connect to it when the port is not 25. I do not have hardware firewall at the moment, which could prevent that.
Any help would be appreaciated!