Update: Somewhat fixed in Apple Mail with Mac OS X 10.7 (Lion). The new default view of messages doesn't have these columns but, the "Classic Layout" option will display them, and the unread column is no longer sizeable. The attachment column still is, but that's forgivable since it does contain text (I suppose someone out there likes to see that count). So, I'll call this fixed.
The message listing in Apple Mail has a few columns for showing things like: whether a message is flagged or not ("Flags" column), whether it is unread ("Message Status" column) and whether it has attachments ("Attachments" column). The first of these cannot be resized, but the latter two can. This is unhelpful:
There's no need to display the number of attachments — most of the time it is misleading because often they're just images that are part of some email signature or something. But the point is, no one needs to resize these columns... they should just be fixed-width, like the "Flags" column is.
