Hey CT - From the information you have provided, it would appear that:

* Some of your customer's emails have been identified as spam. Once enough emails, from the same address, have been identified as spam, that address will then be blacklisted altogether. (554 error = SPAM).

* AT&T are most likely in the clear and the addresses would have indeed been blacklisted by Yahoo.

Not too sue you will have any joy with Yahoo either; their spam system would be automated and applied across the board.

There is something, some mention or terminology contained in your customer's emails which is causing them to be identified as spam. Setting up new email addresses or changing over to a different webmail service would only provide a temporary solution; most services would use very similar parameters for identifying spam. Your customer would need to identify exactly what term or phrase in the emails is tripping the Spam alarm and either not include that any more or find a way of re-wording it.

HTH,
Cheers.....Jim

Yep CT, I'm sure you are right. Unfortunately there can sometimes be a fine line between what these Spam systems see as spam and the actual intent.

A phrase in the email such as 'Special Offer' or something similar will often [unintentionally] ring the Spam alarm.

Yes CT, that would definitely be a possibility. What led me to to believe it was unlikely was this from your original post: [i:uwgfzwvm]"I have a customer that has had[u:uwgfzwvm] many [/u:uwgfzwvm]of its email accounts blacklisted"[/i:uwgfzwvm]

It would be rather unusual for "many" email accounts, all from the same client, to be hacked. Much more likely your customer's emails are being flagged as spam. These spam identification systems can be pretty aggressive; the emails don't even need to actually contain any suspect material, just sending out relatively large numbers of emails, all at once, from the same email address can trip the alarm.

I am assuming the "blacklisting" means that the customer can no longer log-on to the affected Yahoo accounts??

If that is the case then changing the passwords would not be possible. So the only other course of action would be to contact Yahoo (which you have already done) and hope they can sort it out for you.

In the meantime, if you do suspect the accounts may have been hacked, I would be scanning the host machine(s) for any rootkit or spyware; use programs such as MBAM and/or SAS as well as Sophos Anti-Rootkit and any resident security software.

Also, have a read through [url=http://www.pcnsdfw.com/blacklisting.html:uwgfzwvm]HERE[/url:uwgfzwvm] CT, it may provide some insight.

Cheers.....Jim