AT&T has an email -> MMS gateway that you are supposed to be able to send email to, that will then get delivered as an MMS to the phone. For any other mail server this works as is.
What is especially strange is that if I send a mail from the bash interface at the CLI to the mms gateway, it is delivered to my phone. So I know it's not an IP block.
But when I try and send a test alert from XI, it never makes it. Further evidence of AT&T's filtering IMO.
I almost wonder if it's flagging on something in the header, like
Or some other tag... like https://drupal.org/node/321857X-Mailer: PHPMailer 5.1 (phpmailer.sourceforge.net)
edit: it's not the PHPMailer bit, I removed that and still filtered.
edit2: tried switching from sendmail to postfix, no change