Lost mail accounts after OS 10.11 upgrade

I lost my ability to send emails from my iCloud account, only. They would go into the Outbox, then when asking for password upon attempting to send I got the"Unable to Validate" response. Re-entering the correct settings in the Mail preferences did nothing. I ended up replacing/restoring the accounts preference file in the V2 folder of MailData in the Library folder with the one from yesterday via Time Machine. That worked for me.

Otherwise all seems fine.

iMac 27, Mid 2011 up from Yosemite.

Ditto

See my post here Apple mail accounts & boxes Missing

See my post here Apple mail accounts & boxes Missing

Sadly the V3 folder on my laptop contains dozens of mailboxes, many of which are duplicates of all the other mailboxes, etc. Even after reimporting many of them they require massive amounts of copying mails and deleting sub-mailboxes, etc.

To make matters worse, Mail.app crashes if you run out of disk space whilst reimporting them...

Have had same issue, all my email accounts didn't get migrated into El Capitans Mail. Found though that all the data was in user/library/Mail/v3 it just hadn't imported the accounts. Found if I re added the accounts, so long as they had the same name, everything reappeared. But it is a pain, and disappointing.

Curiously my mail is now looking up some old accounts that don't appear in either Mail.app->Accounts or System Preferences->Internet Accounts.

Anyone know where El Capitan stores the plist for these as I'm guessing that's the only place I'm going to be able to delete them?

In my case, all the data got moved to the V3 directory, except for one file:

Accounts.plist

That still contains all the account data. I don't know how to get Mail to import those data.

(To add insult to injury, Mail somehow finds a certificate problem with mac-services.apple.com when I try to re-add my accounts manually, preventing any new account setup. Luckily, I have PostBox and Airmail 2 to save my bacon...)

I had the same problem. Lost 50,000 emails. Accounts where there but no Inbox, Sent or Draft content. I solved it by going into each Inbox and Selecting Menu item "Mailboxes" -> "Rebuild". At first it appears that nothing is happening and then eventually everything returns. I had to rebuild each account at each level (Inbox, Draft, Sent). No problem since. I'm disappointed in Apple with the lack of robustness these days.

Odd that Apple hasn't formally acknowledged this as a problem... some folks have reported that in conversations with Apple Support that this is a "known" issue.

Hopefully there will be an update to address this issue. I have another Mac that hasn't been "upgraded" yet, so I am still able to access my 3 mail accounts (2 x IMAP and 1 POP). I'll wait to see if this issue is resolved in a patch before upgrading that machine. I can't risk not being able access my email.

I had same problem but fixed by going to main preferences and logging out of iCloud deleting all email and contact on Mac and then logging back in. This corrected on all 3 computers in my house which had email screwed up. You have to close the email program and wait about 10 minutes to reopen. Was very frustrating but now fixed.

This is the route I went as well. Re-imported from ~/Library/Mail/V3/*account*/*box* for each account and folder (Inbox,Sent,etc). It was somewhat manual since each import appeared as an Imported folder, but then I just Moved the needed messages from there to the appropriate folder. Looks good so far, but clearly the El Capitan migration was at fault here.

Grrrr, most basic of things one would think, preserve and transfer ALL email accounts, settings and local folders. All have gone. Have copied the .plist file from V2 to V3 and activated all the accounts, but they now all show as IMAP accounts instead of POP3 accounts (although there are folders named POP-"various names" in the V3 folder) and will not connect to the mail server nor download any emails, and I seem to have lost ALL my previously downloaded and sorted emails/local folders. Strangely the Rules are still in place under preferences. Have tried to import the .mbox files but Mail daemon tells me there are no valid .mbox files to import despite them being in the mail/v3/mailboxes folder. So frustrated as cannot see a way to restore the information that is clearly there on the hard drive.

Don't try to import your old mailboxes using the .mbox option, use the top option, I think it just says Apple Mail.I had the same problem with being told they weren't 'valid .mbox files'.

I have also found several old inactive mail accounts that don't feature in the Mail->Preferences->Accounts or System Preferences->Internet Accounts but when you use the Mail->Connection Doctor it says it can't connect to the SMTP element of those old accounts.

On a different note I had a phone call from Apple Support in the US yesterday and they are looking in to the problem.