Mail lost all settings and does not allow to see old messages

Question

One day I launched mail and it appeared as if it was starting for the first time. I aborted the procedure, rebooted and relaunched mail but again. So I regave all the necessary parameters. Then I noticed that Mail had actually kept all the previously custom folders but would not show -a part from the most recent ones- all older messages in Inbox. I looked into Library/Mail/mailboxes and found the missing messages but whenever trying to reimport them into mail got the message that Mail could not find messages in a format acceptable to Mac OS. Actually the messages can be opened with the Mail (but not imported) and have extension .emlx
As an addtional info, the problem appeared shortly after I had switched hosting service but I do not see how this could have affected mails sitting in my hard disk.
It should also be noted that I am receiving and reading new mails without problem.
Any suggestion on how to recover my messages and have them again accessible in my Inbox?
Thanks.
Stefano

Answer 1

What you’ve described could be the result of having set up the account differently and Mail not recognizing the account folder already present in ~/Library/Mail/ — see below a more thorough description of this particular issue. If this is a POP account, the most recent messages in Inbox might appear to have been preserved because they were still on the server and Mail downloaded them again as if you had never set up this account in Mail before.
Under some circumstances (e.g. lack of available disk space, filesystem corruption, repeated crashes), Mail may discard the current ~/Library/Preferences/com.apple.mail.plist preferences file and create a new one. This file is where all the account settings are stored. As a result, all your non-.Mac account settings (but not the messages themselves) are lost. If you had a .Mac account, its settings would appear to have been preserved because Mail would set up that account automatically using the System Preferences > .Mac settings.
Verify/repair the startup disk (not just permissions), as described here:
The Repair functions of Disk Utility: what’s it all about?
After having fixed all the filesystem issues, if any, and ensuring that there’s enough space available on the startup disk (a few GB, plus the space needed to make a backup copy of the Mail folder), quit Mail if it’s running, and make a backup copy of the ~/Library/Mail folder, e.g. by dragging it to the Desktop while holding the Option (Alt) key down, just in case something else goes wrong while trying to solve the problem. This is where all your mail is stored.
There are three ways you could have solved this problem (#2 is what you did):
(1) Restore ~/Library/Preferences/com.apple.mail.plist from a backup if you have one. Mail shouldn’t be running while you do this.
(2) Set up your mail accounts again. If given the option to import existing mailboxes or something like that, don’t. Just enter the account information and Mail will automagically rediscover the data in ~/Library/Mail/ when done. You’ll also have to re-configure most of your settings in Mail > Preferences. For spam-related security reasons, the first thing you should do is go to Preferences > Viewing and disable Display remote images in HTML messages if it’s enabled.
(3) Mail may have renamed the old preferences file to com.apple.mail.plist.saved. If that’s the case, you may try trashing the new com.apple.mail.plist and renaming the old com.apple.mail.plist.saved back to com.apple.mail.plist. Again, be sure Mail isn’t running while doing this. Given the circumstances, I would expect com.apple.mail.plist.saved to be corrupt, but apparently that often is not the case and the settings can indeed be restored by just renaming it back to com.apple.mail.plist.
Note: For those not familiarized with the ~/ notation, it refers to the user’s home folder. That is, ~/Library is the Library folder within the user’s home folder, i.e. /Users/username/Library.
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For each mail account, Mail creates a folder in ~/Library/Mail/ whose name starts with the account type (POP, IMAP, Mac), followed by the account username and the incoming mail server.
When re-creating com.apple.mail.plist, setting up an account with a username and an incoming mail server that exactly match one of the already existing account folders in ~/Library/Mail/ causes Mail to automatically recognize and reuse that account folder. If the username and/or the incoming mail server are different and don’t match an already existing account folder, however, a new account folder is created from scratch, that account behaves as if it had never been set up in Mail before, the old account folder is simply ignored, and the messages it contains become inaccessible other than by manually importing them or setting up the account again.
If you have more account folders in ~/Library/Mail/ than accounts in Mail > Preferences > Accounts, that means some of the account folders have been created anew whereas others are being ignored by Mail (and hence, you don’t have access to the mailboxes and messages stored within them). You can, however, import their contents doing File > Import Mailboxes, choosing Mail for Mac OS X as the data format, and following the instructions. You can get rid of the unused account folders afterwards.
Pay attention to the instructions that Mail displays when choosing Mail for Mac OS X as the data format. In the next step, Mail wants you to select the folder that contains the mailboxes to be imported (i.e. the folder where the *.mbox folders to be imported reside), not the *.mbox folders themselves nor the Messages folders within them. If you select the wrong folder, Mail says “No valid Mail for Mac OS X files were found” because it cannot find any *.mbox folders within the folder you’re selecting.
Alternatively, you may try re-creating com.apple.mail.plist again and this time use the exact same username and incoming mail server that Mail used to name the old account folder.