As you can see, letting a mailbox grow indefinitely is a really bad idea. If you’re just starting to experience the problem, doing what the
Overstuffed mailbox is unexpectedly empty article suggests might work. If you’ve let the problem to become worse over time, however, it may be too late to solve it as described in the article, but you may still be able to fix it as follows:
1. Quit Mail if it’s running.
2. Assuming this is a POP account, in the Finder go to
~/Library/Mail/POP-username@mailserver/.
3. Locate
INBOX.mbox and move it to the Desktop.
4. Open Mail. A new empty
INBOX.mbox will automatically be created within the account folder, and this will allow you to continue using Mail normally while trying to solve the problem.
Although
INBOX.mbox appears to be a file, it’s actually a special kind of folder (a package) that contains several files. Ctrl-click on
INBOX.mbox and choose
Show Package Contents from the contextual menu to see the files it contains. Of these files,
mbox is the most important and is where all your messages are stored. What’s the size of that file? Depending on its size, you may or may not be able to directly import it back into Mail in the next step.
An
Incoming_Mail file may also be present, in which case it might contain messages that Mail couldn’t transfer to
mbox.
Incoming_Mail is also a standard mbox file like
mbox proper, just named differently, and can be imported back into Mail in the same way.
5. In Mail, do
File > Import Mailboxes and follow the instructions to import the
INBOX.mbox that’s on the Desktop. I’m not sure what the import options available in Mail 1.x are, but you should choose
Other / Standard mbox or something like that, so that Mail looks at the
mbox file only (and
Incoming_Mail, if present) and ignores the other files in the package.
If Mail doesn’t let you select
INBOX.mbox in step 5 because it’s a package instead of a plain folder, rename
INBOX.mbox to just
INBOX (i.e. remove the
.mbox suffix) so that it becomes a normal folder, and try again. You cannot do this directly in the Finder because removing a suffix by normal means causes the Finder to
hide the suffix instead of renaming the file. To remove the suffix from the name, you must do
File > Get Info (⌘I) on the file and change the name there.
If the
mbox file is too big for Mail to handle it, however, you’ll have to break it into smaller pieces. You can do that with an
MBOX Breaker Script available at Allan Sampson’s website, or with
Emailchemy. The former will ignore the
Incoming_Mail file that I mentioned previously, but you may try importing that file directly if it’s not too big or just ignore it if all your messages are in
mbox. Also, if you removed the
.mbox suffix from the name of the mailbox, you may need to add it back again for the script to recognize it.
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. That is, ~/Library is the Library folder within the user’s home folder, i.e. /Users/username/Library.