Fax Recipient not receiving email of tiff file

Fax Recipient does not receive tiff file via email.
FreePBX v
AsteriskNOW distro
Installed res_fax_digium successfully
configured SIP trunk and Inbound Route for Fax Detection - IT WORKS!
sending to Extension with ATA and a real fax machine works!
sending to a Fax Recipient distination fails, there is a tiff file in /var/spool/asterisk/fax but it is not emailed

using PostFix Mail Server already, voicemail delivery to email does work fine
SMTP relay is to smtp.gmail.com and it works without a problem

Any hints on what additional config is necessary to get the received fax to go via email? What would be recommended next places to look for hints?