Q: Mail not working with El Capitan

If you can’t send email using your iCloud account after upgrading to El Capitan then following these steps may help:

• Open System Preferences>iCloud and unclick the checkbox beside Mail to disable it.
• Once this process completes, click on the box to turn Mail back on, and close System Preferences.
• Launch Mail and open Preferences>Accounts. Choose iCloud.
• Set the ‘Outgoing Mail Server’ section to the right to iCloud.
• Close Preferences and launch Mail.

Good advise if your iCloud is enabled in system preferences. Mine is not, no clicking on or off. Two inactive iCloud mail accounts. Impossible to delete or activate, iCloud drive totally disabled. I am able to get all my drive data in Safari on iCloud there.

After I upgraded the system on my 17-inch MacBook Pro to OS X El Capitan, I could still send email, but receiving email in all my accounts became intermittent and a gray triangle icon appeared by each address in the inbox.

I corrected this problem by going to mail preferences, clicking on ADVANCED, and clicking off AUTOMATICALLY DETECT AND MAINTAIN ACCOUNT SETTINGS.

Had same problem.

Solved it by:

Preferences > Accounts > Advanced , and

Uncheck "Automatically detect and maintain account settings"

Uncheck "Include when automatically checking for new messages"

Check "Allow insecure authentication"

ahhhhhhhh...thank you. My mail was coming in 3-12 hours later. weirdest thing. I did have to exit mail and come back in, but I also didn't try to "Get Mail" so that might have worked too.

I've been having the SAME annoying problem and searching forum after forum. THIS EASY LINK BELOW SHOWS YOU HOW TO SOLVE THE PROBLEM. I followed the instructions, restarted my mail app and everything works perfectly now. Please try this easy fix before trying more detailed solutions that may cause you to lose important data.

TRY THIS: http://osxdaily.com/2015/07/05/resolving-mail-problems-os-x-update/

I had some of these issues, and was able, with the help pf a Chat session, to recover my Account settings. I find that Mail still becomes unresponsive for several seconds at random....it seems to be looping internally. I have stayed with El Capitan....

Hi DJC,  My mail problems were solved using some of the solutions given in this post.  Thank you all very much.  Still, sometimes the mail was  a little erratic and hesitant (only a few seconds at a time).  Also my sent e-mail alias kept changing randomly to a me.com address even thou I selected a iCloud.com address.  What fixed this was to go to mail preferences and click on the arrow for alias and select  edit aliases.  This logged me into iCloud mail and in that app a menu appears and under composing I made my iCloud.com address my default.  Everything works great now, no more hesitation or glitches left.

Best of luck: Tom

I really am starting to despair with Apple, there where big problems with Mail App in Maverics, then again in Yosemite.... and now again in El Capitan. Seems like the company have no interest in making an operating system and its apps work properly anymore, just a case of kicking it out the door for some reason. Mail App was incomplete and a disaster in Yosemite and now the disaster starts again 10 steps back from where it left off, I have now no confidence left in Apple.

When opening Mail I find most of my accounts settings have lost their settings, names, email addresses, passwords etc. and when trying to enter this information and being asked to save the information is not saved, it doesn't matter if 'Detect settings' is selected or not. BTW, before upgrading I have unselected 'Detect settings' on all my email accounts because of the time wasting mess Apple created for me after upgrading to Yosemite, why do they think I now want this selected on the accounts I had it deselected on?

Mail is once again a total mess of an application which one would suspect made by a bunch of amature developers but then maybe this is what Apple is becoming with their OS's

This solved it for me - it seems the multiple system upgrades I've installed since 2013 won't work with the El capitan upgrade. 

Re install the original operating system via internet recovery - cmd alt R at boot.    Re install data back up.  Upgrade to el capitan. 

It now works beautifully and faster than before 95% of the time.  Still crashes occasionally...

Good luck....

Had a problem with my IMAP accounts after getting new Mac with el Capitan installed. Could receive, but not send mail. Spent 90 min with cable tech. Turns out because we had 2 e-mail accounts, we had to give the outgoing server for each account a different description. In Mail Prefs, under Account Information, down to the dropbox for Outgoing Mail Server, he had me choose the last choice 'Edit SMTP Server List'. The 'Description' here had to be different for each account, so we added our first names before the word OPTIMUM (our service provider) for each of our accounts. Then everything worked fine. Before trying this, he did have me delete and then add the accounts several times to no avail, but this fix worked. Perhaps someone with more technical knowledge can explain this better. It took the tech 90 minutes to figure out that Apple mail won't let 2 or more accounts use a same-named server, so maybe this could help someone here.

I'm on a Macbook pro 2013.

I upgraded to El Capitan last night and today my mail client would not send mail. No surprise though because my mail client often has problems staying online and configured if there is a problem on my server's end or with system updates. So, I deleted my configured accounts and began to re-configured them. With the mail client app closed, I tried adding my accounts again through the system preferences with no luck. I received the "could not connect to the server" alert. I then googled and found these instructions and they worked!

http://docs.businesscatalyst.com/user-manual/site-settings/email-users/set-up-em ail-on-apple-mail-mac-os-x-el-capitan

Where the directions say: "4. Enter for Incoming and Outgoing Mail server:mail.worldsecureemail.com "

Make sure to enter your host's mail server not the one mentioned in the directions. Just wanted to note, cause it looks like it wants you to enter what it says in the directions.

I noticed that it might help to add accounts from inside the mail client app while it's open as apposed to outside of the app from the computer's system preferences. I did nothing different while trying to configure my accounts, but only when I added them through the mail client did they connect.

One thing I noticed is that when you go to compose a new message, the message window no longer has the option to choose which account you are sending mail from if you have multiple accounts in the mail client. So that's weird. I've just been making sure that I'm on the right account I need to be on when I compose a new message and I tested that method, it works. But yeah, el Capitan no bueno.

Hi  Pete, do you also have a fusion drive?  The method you discribed worked for me also and no crashes.

Tom

OK I have now reverted back to my last saved Yosemite backup and kicked El Capitan out, Mail problems are behind me now and it will be a long rime before I upgrade my laptop again.

I never checked the reviews El Capitan had in the App Store Updates section, as I am in Spain most of these are in Spanish although I am using the English version and looking back I now see about 9 out of 10 people who had upgraded to El Capitan have had a lot of problems with it with most of them wishing they had never installed it, I guess I should have read those before installing El Capitan! I know Apple does not pay much attention to whats here but if they really want to get shot of their computer section of sales then the state they have been putting out their OS's out the door in is going to help them. People say there are only a small percentage of people who have problems with the install of El Capitan but thats not what I see from the App store reviews.

Good luck

Same problem on three machines (MacPro, iMac and brand new Air) after the upgrade. Mail crashes with Exchange account enabled. Many hours on phone with Apple tech support (which was wonderful to deal with, but unsuccessful); many CrashData reports sent and analyzed by their engineers. Mail typically crashes on open, then will (sometimes) stay open the 2d and subsequent restarts of the app. On restart, it pulls in new Exchange mail, but won't get new. Turned off Automatic downloading, seems to have helped the crashing issue but does nothing for the inability to get new mail in that account. Apple concluded it was an office365 problem.

Tried office365 support, also quite patient, but nothing to add beyond links to this and similar forum entries.

Only solution was browser access (ugh!) or license Outlook, but the workflow in Outlook is entirely different (and, as a result, frustrating). Please, Apple - figure this out and fix!