System Admin Pro - Email Config "No recipient addresses found in message header"

Hi all,

I’ve got a clean FreePBX stable distro (10.13.66) with a licensed System Admin Pro - but having issues getting outgoing e-mail configured. Any attempts to send triggers the following in /var/log/maillog

postfix/postfix-script[1662]: starting the Postfix mail system
postfix/master[1663]: daemon started -- version 2.6.6, configuration /etc/postfix
postfix/sendmail[3576]: fatal: asterisk(500): No recipient addresses found in message header

There’s only one test extension on the system and it has a recipient e-mail address specified.

Have tried with both Gmail and authenticated SMTP settings just to make sure it wasn’t on the outgoing server end.
Anyone have any thoughts - can’t seem to find anything relevant on-line as the few occurances of this error are usually with manual mail scripts that have incorrect paths or typos.

Did you ever find a solution? I’ve got a FreePBX deployment doing that same thing, but intermittently. Very strange.