maildir-archive is a small utility to archive a Maildir inbox by date. Here's what it looks like if you run it:

joshua@dashnine:~/Maildir$ ~/maildir-archive
maildir-archiver: Opening cur/... done
maildir-archiver: Doing preliminary scan of e-mails... done (15972 mails to archive, 672 too new, 2 invalid)
maildir-archiver: Archiving e-mail... [================================] \ 15972/15972
maildir-archiver: Statistics:
maildir-archiver: All operations performed in 246 seconds
maildir-archiver:
maildir-archiver: -------------------------------+----------
maildir-archiver: Status                         | Emails
maildir-archiver: -------------------------------+----------
maildir-archived: Processed                      |  15972
maildir-archived: Too new                        |    672
maildir-archived: Not an e-mail                  |      2
maildir-archived: Already in correct folder      |      0
maildir-archiver: -------------------------------+----------
maildir-archiver:
maildir-archiver: -------------------------------+----------
maildir-archiver: Folder                         | Emails
maildir-archiver: -------------------------------+----------
maildir-archiver: Archive-2010-Q1-List           |    102
maildir-archiver: Archive-2009-Q3-List           |   2844
maildir-archiver: Archive-2010-Q1-Personal       |    111
maildir-archiver: Archive-2009-Q3-Personal       |   5988
maildir-archiver: Archive-2009-Q4-List           |   3148
maildir-archiver: Archive-2009-Q4-Personal       |   3779
maildir-archiver: Total                          |  15972
maildir-archiver: -------------------------------+----------
joshua@dashnine:~/Maildir$

Although it's never done so for me (that I know of), I can't guarantee that it won't eat any of your e-mail. If it breaks, you get to keep both pieces.

Patches? Joshua Wise <joshua@joshuawise.com>