No external email client can access my att.net email

I've been using Thunderbird for years, both with Comcast and now Uverse (att.net) without problems. Here's a thread that might help some. http://forums.att.com/t5/Features-and-How-To/Mozilla-Thunderbird/m-p/2668993/highlight/true#M23011

Thanks, and actually before I wrote my question, I did locate, read,
and tried to follow the advice offered at:
http://forums.att.com/t5/Features-and-How-To/Mozilla-Thunderbird/m-p/2668993/highlight/true#M23011

and also:

http://www.att.com/esupport/article.jsp?sid=KB401568
http://www.att.com/esupport/article.jsp?sid=KB401570

and

http://www.ehow.com/how_6822136_set-mail-plus-forward-pages.html 

which led me to EITHER ATT.NET or YAHOO.COM pages for mail OPTIONS that

clearly said 'If you want to check email from this att.net Mail account in an email client like Outlook, visit "Pop & Forwarding" on the left.' - and several tutorials SHOWED the 'Pop & Forwarding' choice on the left side of the screen.

THE 'POP + FORWARDING' OPTION IS NO LONGER VISIBILE AT ATT.NET / YAHOO.COM MAIL OPTIONS.

THE WEBMAIL AT ATT.NET DOES NOT GIVE ME THE SERVER - CHOICE TO PERMIT POP ACCESS. 

I tried EVERY recommended and possible variant trying to set up a simple Windows Live Mail account.

Primarily:

Incoming (POP)                     pop.att.yahoo.com
Outgoing (SMTP)                 smtp.att.yahoo.com (requires authentication)
User name:                         (my email address)@att.net
Logon using    authenticated POP (APOP)
Logon using account name        (my email address)@att.net
Logon using Secure Password Authentication
Incoming mail server:             POP3
Incoming/Outgoing User Name:     Full AT&T email address, including domain (e.g., test@att.net, test@bellsouth.net)
Incoming mail port #:             995, secure connection (SSL) checked
Outgoing mail port #             465, secure connection (SSL) checked

Then, when I got back error messages such as:

Unable to send or receive messages for the Att (______ ) account.
Windows Live Mail couldn't log on to the email server using authenticated POP (APOP).
Contact your email provider and verify that it supports authenticated POP. ...

So I tried all available authentication and NON authentication options. 

I still could not send or receive any email. 

I do believe for new users, like myself, the POP access to ATT.NET to allow me to use

any email client has been crippled by AT&T or YAHOO at the server level. 

Any other new users running into this dead end wall?

Anyone working at AT&T willing to step up and help?

thanks -

Your experience and conclusions mirror mine. I tried to go back to my blackberry bold 9700 from an iphone 3gs. Spent hours trying to figure out why att.yahoo mail would NOT work, no matter what I, or AT&T support did to "fix" it.  My regular windows live hotmail account worked just fine, but not my AT&T email - no way/no how.  I concur that Yahoo does not support that mail format, perhaps an attempt to leverage everyone into "the cloud".  AT&T tech support said that Yahoo mail was a known issue and they were "working on it" - but message threads go back at least 3 months on these issues so I would begin to wonder whether that want to fix it.

I ended up back with 3GS, a nice  multimedia device with cool software but lousy phone call quality. The opposite of Blackberry, with excellent hardware but lousy software and OS - including 6.0XXX. Good luck with your quest.