SIP provider set (prefix)

I’m fairly new at this, I’ve setup about 4 Asterisk systems using ZAP harware, but never a complete VoIP solution. That’s what I have here… I’m trying to setup a Asterisk box with a ATA and seperate incoming and outgoing VoIP providers. Following known documentation I have made the incoming work, but I cannot get the outgoing working. The provider has supplied me a email address and a prefix. How do I tell Asterisk to use this prefix?

Thanks in advance…


I’m wondering if the lack of responses means this is a dumb question… can some please refer me to an example somewhere?