have you setup a webmail? if yes, can you access it at home?
i tried to telnet my remote server using my macintosh
telnet x.x.x.x 25
our email server is also hosted in Linux, if i'm in the local network i can telnet to 25 but if i'm outside the office i can't telnet to it.
but our email server is working fine, I don't want to deep dig into this. I was not the one who started this from scratch.
i'm just sharing with you, that even though you can't telnet to port 25 if the settings are set correctly on Postfix config it should work fine.
i'm not familiar with postfix, hope someone can help you out.