Every now and then Mail.app’s ~/Library/Mail folder deserves a spring clean.

There are at least four ways to reclaim disk space from Apple Mail:

1. Kill duplicate attachments. Adam Jury has posted a nice systematic method of trimming out all the attachments from your old emails. As he points out, many of them only duplicate files that are stored elsewhere on your computer anyway. Lots to slash and burn there.
2. Empty your Attachments folders. In addition, Mail 2.0 stores some attachments that you have opened or edited in a folder named ~/Library/Mail Downloads. Depending on your settings (see the fifth and sixth drop-down options in Mail > Preferences > General), Mail.app may store things in there forever. Prune without mercy.
3. Trim Mail’s SQLite database. Mail’s internal database is by far the biggest file in your Mail folder. Over time it gets bigger, more bloated and a bit cranky. You can delete it and force a rebuild which will produce a much smaller file and — added bonus — a speed bump. You can read about this in an earlier Hawk Wings tip.
4. Clean out pre-Tiger files. If you were using Mail when you upgraded to Tiger, there may be useless files in your Mail folder that you can safely remove. I cut down the size of my Mail folder by 25% doing this. The Apple technote referred to in this earlier tip explains how to do that.

Needless to say, all of this is best done after you have quit Mail and backed up everything first by dragging your Mail folder from the Finder onto the Desktop. Just in case.