22:05:58 <lvlinux> Ysean: it's the 'fax' kazoo_app that has to be running to receive SMTP on port 19025. Generally you would have a Postfix or other SMTP server functioning as a relay and forwarding messages to that. I use Postfix, which sends to HAProxy, which load balances (and failovers) requests to the Kazoo fax app on my servers.
22:23:11 <lvlinux> Freeswitch doesn't need anything extra as the fax kazoo_app just works with ecallmgr to get FS to send, and the fax app stores the PDF or TIFF temporarily where FS can access it.
22:23:26 <lvlinux> Kamailio has no clue about fax; it just sees a SIP call.
22:24:37 <lvlinux> Your SMTP relay (Postfix or whatever) can be on any server, it doesn't have to be on the same machine that the fax kazoo_app is running on.