Verify/repair the startup disk (not just permissions), as described here:
The Repair functions of Disk Utility: what's it all about?
If that’s what you want, you may set up Mail again from scratch and import your mail back afterwards without losing anything as follows:
1. Write down your
Mail > Preferences > Accounts settings or take screen shots of them.
2. If you have a .Mac account and .Mac synchronization of Mail data is enabled either in
Mail > Preferences > General or in
System Preferences > .Mac, disable it before proceeding.
3. Quit Mail.
4. In the Finder, go to
~/Library/. Move (not copy) the entire
Mail folder out of there, to the Desktop.
5. In the Finder, go to
~/Library/Preferences/. Locate
com.apple.mail.plist and move it to the Desktop.
6. Open Mail and set it up again from scratch. If given the option to import existing mailboxes or something like that,
don’t. Just enter the account information and check that everything works fine.
7. You’ll have to re-configure some of your
Mail > Preferences settings. 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.
8. If Mail works fine now and you had any messages stored in local mailboxes, do
File > Import Mailboxes, choose
Mail for Mac OS X as the data format, and follow the instructions to import your mail from the old
Mail folder that’s now on the Desktop. Import the
Mailboxes folder first, then each of the
POP-username@mailserver account folders.
9. If .Mac synchronization of Mail data was enabled at the beginning, enable it again, go to
System Preferences > .Mac > Advanced, click
Reset Sync Data, and choose the appropriate options to reset the Mail data stored on the .Mac server with the data locally stored on the computer, i.e. sync data must flow from the computer to the .Mac server.
As a result of doing the above, some messages may be duplicated. Andreas Amann’s
Mail Scripts has a
Remove Duplicates script that you may find useful.
Do with the imported mail whatever you wish. You may move the messages anywhere you wish and get rid of the imported mailboxes afterwards.
If all is well and you don’t miss anything, the files on the Desktop can be deleted, although you may want to keep them for a while, just in case.
Note: For those not familiarized with the ~/ notation, it refers to the user’s home folder. You can easily locate any of the folders referred to in this post by copying the folder path here, doing Go > Go to Folder in the Finder, and pasting the folder path there.
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It could be, however, that there is nothing wrong with Mail on your computer, in which case setting up Mail again from scratch would accomplish exactly nothing.
What type of mail account is this (POP, IMAP, .Mac)? If POP, what are your
Preferences > Accounts > Advanced > Remove copy from server settings?
Sometimes messages left on the server clog up the account there, or Mail chokes on a message it cannot download and that prevents it from downloading the rest as well.
Try removing from the server messages that have already been downloaded and/or the first message not downloaded yet (i.e. the message that Mail appears to be choking on).
You may want to try to download those messages with another mail client such as
Thunderbird first, to avoid losing them — and use
Eudora Mailbox Cleaner to import them back into Mail afterwards if you wish.