unable to send emails; smtp error message

Really this has nothing to do with the OS, even if upgrading the OS broke it. It is a Mail settings problem or the Mail program itself.

Create a New account in the mail program with all the correct setting. You may have to delete the original account to be able to do this using the same Username and password. So make sure you Back Up all the mail that you now have.

If that doesn't work then switch to a REAL Email program as the one that comes with OS X is the worst.

Well that update may of updated the Mail program which, even though it is included with the OS, is not really a part of the OS. It is a separate program.

If you read these forum you will find many many posts about how poor an Email program Apple/Mac Mail is. Some have no problems, many have numerous problems.

Mozilla Thunderbird.

Have you tried using Show Detail in Connection Doctor (Mail > Window > Connection Doctor > Show Detail) to see how the connection failed? That might lead you to a solution to your particular issue (as opposed to whatever issues other users may have seen).

There is nothing wrong with Mail, Apple's email program, despite what others might say.

All e-mail clients are sensitive to having the correct setup information entered into their configuration setup. They have pretty much the same inputs.

Verify that your username is entered correctly. In most cases it's everything to the left of the @, sometimes it's the whole e-mail address. Also, always make sure that after you make changes to the configuration settings that you not only save the results, but that you also Quit, not just close the open window, the e-mail application and restart it.

Often e-mail clients offer automatic configuration assistants that depend on typical conventions. That's why you may have to adjust some of the settings.

Example: When I worked for the Federal Govt., we used Microsoft Outlook, it configured the user name iaw convention and entered everything to the left of the @. This didn't work though because our IT department mandated the use of our 7 digit login ID used eleswhere within the Government.

The OP stated it was working and then just stopped working. After an Update. This is a common problem with Mac Mail. One day/minute it works OK the next day/minute it doesn't. Just do a search on these forum for Mail problems. You will get pages and pages of problems.

Fine, but millions of people are using Mail with no issues. It might be worth trying to resolve the issues rather than using that piece of crap Thunderbird program that you're recommending. IMHO.

If these are imap accounts, delete them and put them back.

Did you try using your whole email address for the user name?

Teal wrote:

No they're POP (AT&T) accounts. Not a big fan of AT&T but my wife doesn't want hers changed to something else so for the time being trying to resolve this SMTP issue in Mail.

Thanks

About the only thing you can do is Delete these Account then Recreate them. I also use the ATT Yahoo Mail system for 3 of my email addresses and just did a test from one of them to my Gmail account and had no problem sending through the SMTP.ATT.YAHOO.COM servers. But then I am using Thunderbird as an Email client.

Just try it for the SMTP section only.

Try different SMTP settings. Remember to save the settings and to quit and restart Mail.