Axis32

https://support.google.com/a/answer/60751?hl=en That should show you how to whitelist your internal domain

Apologies for Thread Necro but I was searching for good ip fax alternatives to see if anybody was using them. So for best I've found is Stonefax....but I digress. Hooking into a virtual sip server isn't tricky at all. I do this with all of our fax machines using the SPA112 Cisco SPA112 2-Port Phone Adapter - Cisco They are around $40 each and you register them with the sip server over ip and then plug your analog phone/fax machine into the phone port...takes about 5-10 from start to finish.