Q: Lost email since 10.11 upgrade

Encouragingly Apple has contacted me about this issue with a case number of 664092518.

Do they have a "fix" for you ?

Same problem here.  Waiting with anticipation for an answer.  I like El Capitan so far, but if this doesn't get sorted, then it's back to Yosemite.

It would seem they dont know how to fix this 

Hi

I solved importing .mbox (going Files/Import mailbox from Mail). In order to access mailboxes, you should go Library/mail/V3/POP-"my account"/

Remind you that Library folder is hidden. In order to see it, go to Finder click on the menu "go" and click ALT button in your keyboard. Then Library will magically appear.

You will have INBOX.mbox, Sent Messages.box, etc in the folder located at Library/mail/V3/POP-"my account"/

Copy all those files into another folder (if you leave there Mail won't let you import them).

From Mail go to File/Import Mailbox and select the for example, INBOX.mbox from the folder you created. Mail will import it and store into a folder called Importation. You can move them all to your inbox. Done.

Proceed same way with the other files.

I solved doing it.

I only have the problem that Mail doesn't sound when I receive emails....if you know how to solver it, I will appreciate.

Sorry to say: I got the same problem with Yosemite since Sept 30th. Keeps changing the port numbers and keeps forgetting the SMTP password.

I did not try to remove and re-install all accounts yet, but removing/re-installing the pop/smtp account in question did not help. German Apple support tried to fix this problem with me on the phone, but we gave up after 2 hours. Re-installing Yosemite (not clean) did not help either.

The only thing that worked was creating a new user and installing the email account there. I'll try to erase and re-install all my email accounts tomorrow, let's see if it will fix the problem.

haha, so you delete all your (old) mails ... with this action. attention !!!

Ha Ha, only those who are still using POP3 - not with IMAP-accounts. There are many reasons to use IMAP - especially when you have several devices! So it's time to change to a "modern" email-account! Ha Ha!!!

In my case Mail got stuck in rebuilding the mail boxes. Any idea what to do in this case?

Most important question is how to get the previous emails back. I can't find any email received and send.

Have you before pop3 or imap accounts?

Pop3: when you have a backup, .. .copy ~/library/mail/v2 back to the ~/library/mail/ ....then Import mail

thats true, pop3 user lost all mails ... local or archived mailboxes too.

as you're installing NEW accounts your mac will most probably keep the old mails in the library, you just can't see them in Mail. there is a way to re-import these mails, it's described in this discussion by mochnacs, just scroll a little bit.

I have really tried with this, but I am no "techie" and I can't find anything in the library       My storage shows I have loads of emails, so they must be somewhere

Just started another install on an iMac. If Apple Support is reading this: Will let you all know over here if mail upgrades normal or not and leave the computer in its finished state after installation so you can have a look at the logs.

Cheers,
Luc