Fixing Mail.app's Recent Mail Addresses Problem

I had noticed for a while that somehow my Mail.app’s “recent mail addresses” list was not updating (I never seemed to get any of my recently used addresses in Quicksilver). Today I noticed the following error message in /var/log/system.log:

Mail[365]: AddressBook failed to save: Error Domain=NSCocoaErrorDomain Code=259 UserInfo=0x10c9a810 “The file MailRecents-v4.abcdmr€ could not be opened because it is not in the right format.” ({\n NSFilePath = “/Users/dza/Library/Application Support/AddressBook/MailRecents-v4.abcdmr”;\n NSUnderlyingException = Fatal error. The database at /Users/dza/Library/Application Support/AddressBook/MailRecents-v4.abcdmr is corrupted. SQLite error code:1;\n})

While trying to figure out what was wrong, I discovered that the file for some reason had an ACL that prevented everyone (including me!) from modifying it:

~/Library/Application Support/AddressBook $ /bin/ls -lea MailRecents-v4.abcdmr
-rw——-@ 1 dza staff 102400 Feb 4 2008 MailRecents-v4.abcdmr
0: group:everyone deny write,delete,append,writeattr,writeextattr,chown

So I removed the ACL:

$ /bin/chmod -a# 0 MailRecents-v4.abcdmr

And the error is gone! The file was not corrupted, but Mail could simply not write to it. The puzzling part is how did that ACL end up there…