Q: Mail not working with El Capitan

I could not send emails after updating to el capitan.

Found out that the Mail Server Port #s were changed, changed them to the original port #'s.

Works great now.

How do I find the old/new port #s?

Thanks!

I contacted my website developer. he had the numbers.

It was a Gmail account

I would try your service provider and go from there.

Thats about all the help I can give

Hope that helps.

I, too am on gmail but don't have a personal wizard to help with this - I'll ask around though and thanks!

I have the problem with AOL.  It's irritating, but I usually just close the error message and it downloads my new mail anyway.  If it doesn't download it, I close the email program and open it again.  If it comes back and still wants to verify my address and password for AOL, I reboot.  As I said, it is annoying, but I am getting my mail. 

Sometimes it hangs on a send mail, but I just send it again and it goes.

I had the same emails problem when Maverick arrives, and lost two days to fix it, just getting back to the former system.

I had Maverik with my New Mac book pro then, with a technician checking all

On May 13th, I updated El Capitan and read carefully before all possible problems, almost one year after the first release

I had issues with wifi, probably possible to solve. I connected with my mobile to check, it was working. But then the main issue was with the emails: freezing, not sending

I did not spend time and came back after 40 minutes to 10.10.5. I will wait the next Mac Book Pro this Summer to pass to El Pirata (mas que Capitan).

But is it possible that each system upgrade by Mac create problem with mail ?

I just downloaded El Capitan 10.11.3.  Mail does not work as you all said.  I happen to also have on my MacBook Pro Outlook:Mac2011 version 14.6.2 and it works perfectly.  So, this really does appear to be two Apple software packages not getting along.  I have rarely ever used Outlook on this computer, but will do so until Mail is fixed.

Update on May 13, 2016.

I removed my mail account in Apple Mail and then added it from scratch.  It works perfectly now.  I noticed the "incoming mail server" information was different between what it was (in the account I removed) and what it became (in the account I added).  This was all automatically put into Apple Mail by my email provider just by me providing the appropriate email address and password.  It could be true for others that their email accounts actually have some difference in the root settings that may not be completely obvious.  I thought I would share with everyone.

The problem was the Apple reworked Mail for El Capitan, and then didn't prepare those upgrading that they needed to have taken additional precautions beforehand. Fairly widely documented. The problem was even more exacerbated when those like me upgrading from 2 versions previous.

Me too and it's 8/19/16 on a brand new machine, so no Time Machine to refer back to.  It's alarming this is a common problem dating back to Sept 2015.