Graham Barr <Graham.Barr@tiuk.ti.com>
    + this would be much harder to write if MailTools didn't already
      exist
Cary Evans <c.evans@clear.net.nz>
    + provided very good feedback on first pass at the maildir interface
    + wrote File::Sync
Chris Faylor <cgf@bbc.com>
    + first person to be brave enough to write an MUA in Mail::Folder
    + suggestions and bug reports
Nick Ing-Simmons <nik@tiuk.ti.com>
    + several suggestions and bug reports
Andreas Koenig <andreas.koenig@franz.ww.tu-berlin.de>
    + reminded me of the need for synth_envelope_from and provided the code
    + suggested I make register_folder_interface implicit
    + suggestions and bug reports
Nathan V. Patwardhan
    + suggestions for simplifying the method interface