Your problem could also be that the mail process (Postfix) on your AsteriskNow server isn't being allowed to send the messages through any email servers.
Many email servers do not allow un-authenticated servers or clients to send messages. It was (still is, if they can do it) a favorite tactic of spamers. Spammers would relay their spam through another providers email server.
To combat this, most responsible email server administrators require that a client attempting to send a message to a destination other than their own domain, be an authenticated user of the service.
You may have to setup Postfix, and Cyrus SSL to have it automatically authenticate with a known email server. Postfix, and Cyrus SSL should both already be loaded with AsteriskNow.
A how-to for that can be found here:
http://postfix.state-of-mind.de/patrick ... rvers.html