My 3CX fax server does not initiate handshake when receiving a call from an Anonymous caller (caller ID blocked). I have several DIDs pointing to different extensions for faxing purposes. So for example I have 16173998217 set to “Send fax to” “email of extension 221 Corey Boyle” This works great as long as the incoming fax is sent from a line that does not have caller ID blocked. If the caller ID is blocked, the fax server answers the line, but never gives tones. I can confirm this with my iPhone by switching “show my caller ID” on and off. If I call with “show my caller ID” set to “on” I hear the tones. If I call with “show my caller ID” set to “off” I do not hear the tones. Any help would be appreciated, as this causes quite an issue for me and my users. A surprising number of faxes are sent from lines with caller ID blocked. I have attached a portion of my server log. You can see an anonymous call at 09:57:15.266 and a normal call at 09:57:48.534.