Q: Mail SMTP (outgoing) does not work after Yosemite upgrade

"I found another forum post on here regarding the same issues with IMAP, and the solution was to uncheck the option under mail preferences -> accounts -> advanced -> and UNCHECK "automatically detect and maintain account settings". I unchecked for all accounts, closed and reopened mail, and every email that has come in to these accounts since I installed Yosemite finally all downloaded. Hope it works for others as well."

I hadn't see your suggestion until after I had tried it as well,  but I also  (randomly) unchecked "automatically detect and maintain account settings" just to see what it would do, and my mail began sending immediately.   I didn't even have to restart the mail client.    I didn't change anything else.    Just unchecked that box and everything started working.   (note--I'm using the default mac email client) .  Also, the box rechecked itself on its own and everything is still functioning fine.   Hope this works for others.

I have gone to the extent of doing a "Clean" install of Yosemite, and continue to have the problem.

I have changed my password on the server, without changing the problem.

Double checked by deleting all mail accounts, and recreating them.

Stuck - until Apple can fix this

I know it looks really too simple, but have you tried the solution directly above your post?   It worked immediately for me after hours of trying to figure it out.   If you have tried that, sorry, I have nothing else : ( 

"uncheck the option under mail preferences -> accounts -> advanced -> and UNCHECK "automatically detect and maintain account settings"

Clean install didn't work for me either. Have a look at iMansun's solution above. This worked for me

Unchecking the boxes did not fix it.

The Accounts.plist file was not updated  - strange that is!

Yes - Now why would I think that unchecking the boxes should have change that setting

Editing the file certainly did -

Thanks everyone

I have been having the same problem as everyone else in not being able to connect to any SMTP servers except for iCloud after upgrading to Yosemite.  After reading the comment from HelicopterJonI discovered that settings made in Mail Preferences were not being written to the Accounts.plist file.  I had to edit it with the correct settings before I could finally send mail on the non-SSL port but I still can't send mail on the SSL port, so I suspect that is a separate problem related to certificates.  It looks like Mail and the Keychain are in need of some serious bug fixing.

Thank you, I had tried so many other things the last few days and nothing worked.  did what you said and it worked right away on my imap issue for incoming mail too.

PERFECT!

Thanks man, that helped a lot!

Excelent!

It did work!

Fantastic solution, I am now sending emails perfectly. Two days completely lost with this stupid issue.

I will certainly drink a beer for you...

I followed those instructions and seemed to work. However, after a while, my account was not connecting again. Help!

Where is Apple support? probably selling iPhone 6's and 6 Pluses, while we cannot communicate with Mail.

After updating 4 out of 5 accounts worked but 1 will not work at all in mail no matter what I do, Send or Receive. Account works through outlook, on ipad and iphone 6.

However after updating my iPhone to 8.1 the smtp on this account is failing. Coincidently one of my accounts that was working on my macbook pro decided to stop sending as mentioned here.

The Helicopterjohn solution fixed this problem on the macbook pro but I have no idea how to do similar on the iPhone 6.

These solutions however have done nothing to fix the one account that won't work at all through mail on either my mac book pro or my imac.

Of course it is the one account I need to use the most, work!

Thanks very much iMansun - that's fixed it for me too.