Are you trying to use a .mac/.me email? If so you have to call AT&T and request to have port 25 unblocked. AT&T blocks it to cut down on spam since most email providers don't use it anymore, but Apple still does for their .mac/.me emails.

If you are using something else, let me know.

here's what I'm getting:

The SMTP server “smtp.att.yahoo.com” doesn’t support  authentication. Please check your account settings and try again.

Select a different outgoing mail server from the list below or click Try Later to leave the message in your Outbox until it can be delivered.
 

no, had it over a year.

how aggrevating... 

You may want to check out this page:

http://helpme.att.net/article.php?item=10918&f_application=macosxmail&action=Refresh

Make sure the ports are configured correctly and that you have SSL turned on. If everything matches up yet it still doesn't work, then there is a tool you can download to have it try to auto configure it.

Thanks...still no luck...nutz...

anyone heard of getting port 25 unblocked?  if that might help?

Well if you are using an @att.net address, you don't need to since it doesn't use port 25 in the first place.

But can you at least access the web mail and successfully send messages from there? That way we'll know if it is something on Yahoo's side or not.

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ret4425 wrote:

here's what I'm getting:

 

The SMTP server “smtp.att.yahoo.com” doesn’t support  authentication. Please check your account settings and try again.

Select a different outgoing mail server from the list below or click Try Later to leave the message in your Outbox until it can be delivered.
 

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http://www.dslreports.com/forum/r19984619-Re-Strange-SMTP-problems

Thanks for all the effort...I can access ATT mail through the Yahoo web page.  This is a Mac thing (I am even able to access and send from my Pocket PC with Pocket Outlook).

I'll tell ya, my life is a series of, "Gee, never heard of that before"...

(sigh)

This is the other message I get, I don't see any rhyme to the why:

The SMTP server “smtp.att.yahoo.com” doesn’t support  authentication. Please check your account settings and try again.

Select a different outgoing mail server from the list below or click Try Later to leave the message in your Outbox until it can be delivered.

Sending from: RT <r@att.net>

Downloading Thunderbird now, read the article, and as usual, Mac does a good job of getting things right (it knew the right servers, SSL settings, port settings, etc).  Everything LOOKS like it does in Outlook, I'm sure I'm missing some minor yet obviously important part to all this...

As a new Mac user I see now the anti-Mac prejudice we suffer!

Okay, that one got Thunderbird working...So it must be some setting in Mac Mail I'm missing or doing wrong...I don't have the same option to uncheck that box like Thunderbird...

Thanks again guys for all the help...

sorry to keep bothering...

this is from the Mac connection doctor.  does this make any sense to anyone?  or am I posting my social security number by accident?  When it finishes it says that it can't connect to the smtp server and check me username and password (I did, of course)...

CONNECTED Aug 02 21:50:18.872 [kCFStreamSocketSecurityLevelNegotiatedSSL]  -- host:smtp.att.yahoo.com -- port:465 -- socket:0x15d874b0 -- thread:0x173d2660

CONNECTED Aug 02 21:50:18.912 [kCFStreamSocketSecurityLevelNegotiatedSSL]  -- host:smtp.att.yahoo.com -- port:465 -- socket:0x173f9b80 -- thread:0x82e0d0

READ Aug 02 21:50:19.537 [kCFStreamSocketSecurityLevelNegotiatedSSL]  -- host:smtp.att.yahoo.com -- port:465 -- socket:0x15d874b0 -- thread:0x173d2660
220 smtp108.sbc.mail.mud.yahoo.com ESMTP

READ Aug 02 21:50:19.583 [kCFStreamSocketSecurityLevelNegotiatedSSL]  -- host:smtp.att.yahoo.com -- port:465 -- socket:0x173f9b80 -- thread:0x82e0d0
220 smtp109.sbc.mail.mud.yahoo.com ESMTP

WROTE Aug 02 21:50:19.628 [kCFStreamSocketSecurityLevelNegotiatedSSL]  -- host:smtp.att.yahoo.com -- port:465 -- socket:0x15d874b0 -- thread:0x173d2660
HELO [173.6.207.127]

WROTE Aug 02 21:50:19.665 [kCFStreamSocketSecurityLevelNegotiatedSSL]  -- host:smtp.att.yahoo.com -- port:465 -- socket:0x173f9b80 -- thread:0x82e0d0
HELO [173.6.207.127]

READ Aug 02 21:50:19.723 [kCFStreamSocketSecurityLevelNegotiatedSSL]  -- host:smtp.att.yahoo.com -- port:465 -- socket:0x15d874b0 -- thread:0x173d2660
250 smtp108.sbc.mail.mud.yahoo.com

READ Aug 02 21:50:19.764 [kCFStreamSocketSecurityLevelNegotiatedSSL]  -- host:smtp.att.yahoo.com -- port:465 -- socket:0x173f9b80 -- thread:0x82e0d0
250 smtp109.sbc.mail.mud.yahoo.com

WROTE Aug 02 21:50:19.806 [kCFStreamSocketSecurityLevelNegotiatedSSL]  -- host:smtp.att.yahoo.com -- port:465 -- socket:0x173f9b80 -- thread:0x82e0d0
QUIT

I guess Sprint could be doing it...guess you can ask them?

What I meant about the IP was my wireless would not work at all (initially) away from home; it was because I had set the IP to look only for the RG (home IP), so it would not release the home IP and kept looking for it, wouldn't connect.  But you were able to connect away from home, so that's not it.

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rightrudder wrote:
change the outgoing port from 25 to 587. turn off SSL. 

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I had the same problem and this was the solution I used.  It has worked well for two months now.