Outlook/Exchange rule to forward emails to AT&T SMS.

I'm using Outlook 2010 Pro with an Exchange server.  I'm trying to set up a rule to automatically forward specific emails to an AT&T phone (e.g., username@txt.att.net) so I can receive alerts.  It seems that I can manually forward emails successfully, but the rule-based forward fails.  I see the forwarded message in the Sent folder, but it never makes it to my phone.  I've set my account on the AT&T side to allow up to 10 SMS message segments.  That should be sufficient for most emails.

Does anyone know if there may be something in the message format for rule-based messages that would prevent this from going all the way through AT&T? 

Thanks.