If you are unable to send email while using another company's Internet service, the cause may be one of the following:
Typically, TFN members who also have an Internet connection from another company, eg for their cell phone or for one of their computers, are unable to connect to TFN's port 25 from that other provider's connection. If you are unable to send email from a computer that is using another company's Internet, check whether the agreement for your Internet connection from that other company allows you to directly connect to external SMTP servers.
In order for your email server to communicate with TFN's, your provider must leave port 25 open for your outbound TCP connections. Unless you have a static IP address, outbound port 25/tcp is probably blocked. If so, you have several alternatives:
you can configure your computer to send email via its ISP's SMTP servers.
You can still set a TFN return address on your messages. Correspondents who check the message headers in detail will be able to see that the message was, in fact, not sent from TFN, but you can make the address in the "From:" field show @torfree.net so that replies will come to your TFN mailbox.
You can use TFN's webmail.
You can use TFN's non-graphical Alpine client, through a telnet or ssh connection.
Sometimes, TFN members who have an Internet connection from another company, eg from a cell phone company, will try to use that connection to send email via TFN's SMTP servers. TFN does not currently support this.
If your computer is using another company's Internet access service, TFN will accept connections from it only to receive email that is destined for TFN users. While your computer is using the other provider's Internet service, TFN's servers will not accept requests from your computer to forward email to destinations outside of TFN.
To send email to destinations outside of TFN, please either connect to them directly, or use the forwarding SMTP servers provided by the company whose Internet access you are currently using.