Cingular emailing problems.

As anyone been having problems with sending email msg's from a cingular
phone in the Oklahoma, Bixby area?

Me and my g/f used to send emails to each other and now although I can still
send her an email to the email version of her number, when she replies to me
it says something similar to 'rejected' and something about the email being
bad. It worked before. I've also sent her an email from my regular yahoo
account and isp account and they get rejected as well. So, the problem is on
her side.

Does anyone have any idea why this is happening and how best to resolve the
problem?

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Remove AT from my address reply directly.