ATT/SBC/Yahoo outgoing mail issues anyone?

My mail from my website was set up fine and everything worked like normal until yesterday. Now it's like they blocked my outgoing mail saying "server does not recognize [email]_____@_____"[/email] I did some searches and found some thing to opt out of the ATT block of port 25, but I have to wait for them to respond to my report and hope it goes through. Anybody else having these issues? I hate it when they change shit and don't tell me. Calling tech support is like calling someone who doesn't even know how to use a computer but has a checklist of things to say in front of them. "Now Mr. _______, does your computer have a power cable?""Ok, is the computer plugged into an electrical outlet."ugghhh.