Starting with SME Server 7.0, you have to use secure connections to send/receive e-mail from outside of your local network. Here's what you need to do:
1. In Thunderbird, select "Tools > Account Settings...".
2. In the left column, below your e-mail account, select "Server Settings".
3. On the right, in the Security Settings section:
a. Under "Use secure connection", select "SSL".
b. Make sure "Use secure authentication" is unchecked.
Note: The port number will change when you enable secure connection. If your server type is POP, it will change from 110 to 995. If your server type is IMAP, it will change from 143 to 993. This should occur automatically; if it doesn't, you will need to manually change it in the box next to the server name.
4. In the left column, at the bottom of the list, select "Outgoing Server (SMTP)". On the right, select your server then click on [ Edit... ] .
5. On the right, in the Security and Authentication section:
a. Make sure "Use name and password" are checked.
b. Under "Use secure connection", select "SSL".
6. Click on [ OK ] , then click on [ OK ] again.
That's it. Thunderbird should now be able to send/receive e-mail on your server from the outside. Note: If you have a firewall between the server and the Internet, you will need to open the secure port numbers (and possibly set port-forwarding rules) to access the server.