Config:
freeswitchtemp /] >>>>> cat /usr/local/freeswitch/conf/sip_profiles/efax-int.xml
<profile name="efax-intf">
<gateways>
<X-PRE-PROCESS cmd="include" data="fax/*.xml" />
</gateways>
<aliases></aliases>
<domains>
<domain name="all" alias="true" parse="false" />
</domains>
<settings>
<!-- efax-01 -->
<param name="sip-ip" value="192.11.11.11" />
<param name="rtp-ip" value="192.11.11.11" />
<!-- efax-11 -->
<!-- <param name="sip-ip" value="192.11.11.11"/>
<param name="rtp-ip" value="192.11.11.11"/> -->
<param name="sip-port" value="5060" />
<param name="nat-options-ping" value="true" />
<param name="all-reg-options-ping" value="true" />
<param name="user-agent-string" value="efaxa4/v1.0" />
<param name="inbound-codec-prefs" value="$${global_codec_prefs}" />
<param name="outbound-codec-prefs" value="$${global_codec_prefs}" />
<param name="inbound-late-negotiation" value="true" />
<param name="inbound-codec-negotiation" value="greedy" />
<param name="t38-passthru" value="true" /> <!-- Enable T.38 Passthrough -->
<param name="fax-enable-t38" value="true" /> <!-- Enable T.38 -->
<param name="rtp-timer-name" value="soft" /> <!-- Helps with jitter and fax transmissions -->
<param name="rtp-timeout-sec" value="300" /> <!-- RTP timeout to prevent stuck calls -->
<param name="context" value="public" />
<param name="inbound-proxy-media" value="true"/>
<param name="proxy-media" value="true"/>
<!-- Disabling SRV lookup because it led to a race condition when SIP return 50x -->
<param name="disable-srv" value="true"/>
<param name="disable-naptr" value="true"/>
</settings>
</profile>