The following is a solution for anyone with AT&T Internet Services that recently started receiving (553) errors when attempting to send email, which prevents any outgoing messages. The following remedy should work regardless of what platform your on or what email client you’re using.
It appears that this problem boils down to AT&T re-branding their web experience (and improving it actually), including the link to Yahoo Mail which they inherited when they took over the shop from SBC. In pursuit of better spam filtering most likely, AT&T is now requiring the “validation” of the email addresses from which you send email. The validation process isn’t that difficult… step-by-step instructions can be found here (you may need your AT&T login email address and password here).
Now there’s also the question of what “port” you set your outgoing mail server to, and this is only for the Mac users. The following came in via email from Jeff in Homewood;
I spoke with you just after midnight regarding a problem with Mac Mail. Just spent about 45 minutes in a chat session with AT&T. End result, the ports for outgoing mail had to be changed back to the old settings. Go figure. Apparently their recent upgrades, which require port 465 with SSL don’t work with the Mac, so change back to port 25 without SSL and the system works.
The first part is right on… for whatever reason, the proper configuration of Port 465 with Use SSL checked… doesn’t work on a Mac… The proper port though, should be 110 as opposed to 25, with Use SSL unchecked. I’m not sure if Jeff just mistyped the number, but I did tests on my machine and setting the port to both 465 and 25 caused authentication problems. That’s on a Mac running Leopard 10.5.2 with Mail version 3.2 (919).
One great improvement with the new AT&T Yahoo mail system is that with this verification of email addresses comes the ability to consolidate all your incoming email (from multiple accounts) to the AT&T Yahoo Online mail interface. If you’re someone who would benefit from this… just enter your incoming mail server with login name and password into your account settings on AT&T Yahoo.