Can not send out fax from voip line?

If you are using VoIP which has modem, you can't send fax obviously. You must connect you fax machine to separate lines directly to your ADSL splitter. But, if you are using like ringcentral, you can still fax via internet using you computer or using your fax machine.

OrangePoint.net also has a solution without having to buy hardware or software. It's call computer faxing.

Onesuite.com has an online fax solution too and it is more reliable and alot cheaper than sending your fax through VoIP lines.

It is possible under certain conditions to send a fax over a VoIP line, but it's proven to be highly unreliable in general, and is "officially unsupported" by most VoIP providers. The issue is that VoIP was designed for voice calls, not modem calls. My company, FaxLogic, and one other I know of, Nextiva, make "adapters" that allow you to connect a regular fax machine to the Internet. Unlike "faxing over VoIP", where the modem signal "rides" the VoIP channel (and generally doesn't work), this is "faxing over IP", where the modem signal is converted into data packets by the adapter, which traverse the Internet (or other IP network) just like any other data packet. It's a reliable system designed specifically for fax, and makes a great compliment to VoIP.