Q: Mail not working with El Capitan

Although the Mail.app client is obviously the main issue, it's possible that there are "extensions" to the published protocols from the *servers* which are confusing the new Mail.app.  I'm not apologizing for them, because this obviously should have been properly Q&A'd!  But it's out now and on people's computers, so maybe this is the case. 

My point is, if you have your email hosted by a company where you have access to someone who *really knows what they are doing*, and *cares about your business*, this might be helpful to you - while also maybe making a new "IT" friend.  Maybe someone local.  They will need to be paid, but at least you have someone you can go to, who is knowledgeable and willing to help out as opposed to making you a number.  Isn't that what the Apple Community has always been about?

That's what I did a few weeks ago. Got the bill last week - nearly £400.00... That's probably about $650.00. I wouldn't mind if he was mending one of my own ****-ups, but I do feel this is Apple's responsability. Still not perfect either...

Did it fix things though?  And now you have someone you can contact?  If so, for many business owners this would be a good thing - especially long term.

I have talked to people at BT, not learners, but their tech department and they say a great many people have the same problem and there is nothing they can do about it, it’s an Apple problem, probably due to synching with iCloud, so it’s getting confuse. There is an updated being beta tested now, s they know there is a problem, which is affecting everyone in a different way, so it’s best just to wait and see. El Captan has caused a lot of problems, there than with Mail, so a lot needs sorting!

Don't anyone get confused with the posts here about hosting companies and their servers protocols being an issue here, the issue is with Mail app after upgrading to El Capitan and not your mail account servers, your email hosting company can't fix Mail app and the mess that account settings get into after the upgrade, those need to be sorted on your computer. Don't waste money trying to get your hosting support try and fix something they can't so these posts don't help anyone fix the upgrade issues.

If your email accounts worked before you upgraded why would your server be the issue if they didn't work after the El Capitan upgrade?

After I re configured my accounts in the mail app and unchecked the "automatically detect and maintain account settings", I can send and receive mail just fine, but when I delete mail, it doesn't go to my trash folder. It seems as though mail can't find my trash folder, as though the folder doesn't exist. It says "null" and that there was an error moving it to the file "null"

Has anyone else had this problem? I unchecked "Move deleted messages to the trash folder" for now so I don't get that annoying box notification every time I delete a message. Right now my deleted messages seem to be going to nowhere. They just disappear when I delete them...so I have to be careful and make sure not to delete something I might suddenly need later.

Louis,

I could be wrong, but I'd guess that marking this problem as "Solved" doesn't help it REALLY get solved. This is a huge issue among many that Apple can't seem to sort out. Its sad when a company that's so far in the black can't properly support its users. Oh wait, that's the way the world works now. Please press "9" to repeat this...

El Crapitan! Wota lota garbage. Meanwhile mail continues to misbehave - sometimes it keeps cyclically reloading read or trashed items so that i have to force quit or even reboot. Then there's the occasional issue with attachments that are blank. As for consistent behaviour across devices (imac, ipad, laptops, iphones) - forget it. As a dedicated and knowledgeable pro user over 27 years i'm appalled. Time for Tim to accept responsibility and fix this post haste without excuses. I pay top money and expect top performance.

My latest work-around with Mail: force quit. As soon as I notice that mail is stuck based on a message like a persistent "Copying mail ..." or similar message in the lower left corner of the window, I do a force quit. When I restart, it seems to be shocked back into behaving for a while. I do this 3+ times a day to keep it running. Pretty ugly bandaid ...

In addition to what rev_apple suggested re atomically detecting and maintaining settings, I also found that the if you have the option "allow insecure authentication" and you're are using a private domain host to receive your emails, this may also cause problems downloading files.

Thus, I recommend checking the box for "allow insecure authentication" 

Wish I would of read this post before I upgraded. After upgrading I could send emails but not receive them.  The connection doctor complained about login

information not being correct. I checked and verified all the setting, they were correct. RE-inputted password, just in case something changed during upgrade no help.....After goofing around for an hour I rolled back via Time Machine. This is disgraceful. Mail is one of the things that should work with no issues....it should just work, that is the one of the beauties of MacOS...simplicity.  This issue is so Windows like and not what we as users expect.

I wish I had seen your warning before I upgraded. First I upgraded the iPhone 6 and it has been nothing but trouble for all 3 iPhones in our household.  I should have known better but I did the el Capitan upgrade and immediately lost my email.  It could not have come at a worse time.  I have wasted about 5 hours so far including a session with Apple support, changed my password 4 times as it kept instructing and  I STILL HAVE NO EMAIL ACCESS. The worst upgrade ever!!! Do not do it, unless you want hours of misery!  I would like to bill Apple for the many wasted hours of my time.  If anyone knows how to actually fix this nightmare please post and while you are at it go get a job at Apple they clearly need HELP!

After El Capital upgrade, my solution was to create an alias of  ..@msn.com with ...@outlook.com .

Problem solved. 

Wow... my entire inbox just "disappeared" ...this is an "upgrade"? 

To delete my entire Inbox?!

This is loss of critical data....

Last Apple-anything I'll ever purchase.

After the El Capitan upgrade all of my Mail messages were blank. I tried rkv_apple's suggestion ("I was able to correct this behaviour by going to Mail->Preferences->Accounts and then for each account in the Advanced Tab I unchecked "Automatically detect and maintain account settings". I then quit Mail and when it restarted it appears to work fine."), and the problem went away.  Thanks, rev_apple.