It looks like Yahoo (who deals with the email for AT&T in your case) feels the same way as Obama^H^H^H^H^HThe Google.
I'm not sure what you can do about it except subscribe twice (once from some other address that also makes it to your mailbox) and set your "real" email address to "no mail" in the Mailman configuration. That way the filtering that your email provider does would never get triggered.
/jordan