Internet service provider requirements
Your Internet service provider may make it difficult for you to run your own server. You should check whether they (or one of their competitors) offers these features:
Port 25
You'll need this port open to (?). You can check whether it's open on this site: http://www.canyouseeme.org/
Port 80
You'll need this port open, to (?). If it's blocked, you may be able to use a non-standard port. (explain).
If your ISP blocks port 80, a commercial service like this one may help: http://www.noip.com/managed-mail
Static IP
You'll need a static IP address. Many ISPs give their customers dynamic IP address. Some ISPs offer static IP addresses for a small fee.
If a ISP tells you that a port is available, but you must opt-in through your router, use this guide: http://portforward.com/english/routers/port_forwarding/Dlink/DI-524/defaultguide.htm
I got this information from the community members here:
http://trisquel.info/en/forum/how-do-i-set-mail-server
