My reply to an email in 2012-03.


> Why is MH mail store format nicer over plain mbox or maildir?

mbox had been the historic format. It comes from a time when mail
messages were only a few lines and were deleted soon. In today's time,
when messages are megabytes in size and are kept for long times
(meaning you have hundrets of message in one mbox) the format has too
many disadvantages. One would never have chosen the mbox format for
today's mail handling.

This leads us the the MH format, which had been invented already in
1977! It is very simple: Store each message (as received, i.e. in
transfer encoding) into one file. Group files in directories, i.e.
make use of the Unix file system. The files are named with ascending
numbers. That's very simple, you see. It's the most simple approach if
you want to have each message in one file. The `.mh_sequences' file is
used by MH to store the name of the ``current message'' and similar
stuff. This is only relevant for the MH tools, but not for the storage
format itself.

The maildir format had been invented much later (in the 90s). It
essentially takes the MH approach and adds some complexity to remove
any need to lock files. Therefore, you have subfolders and the
messages are named with generated sequences and not numbers.

To sum up:

You don't want to use mbox, except as the most general transfer format
between systems and for compatibility reasons.

The MH format is the most simple format, but suffers in the last 10%
(file locking).

Maildir adds 70% more complexity to cover these last 10%. Most people
believe that maildir is the best option.

I'd say that it depends on how you use it. If you likely run in to
file locking conflicts than you should use maildir. If you don't, you
might be better off with the very perfectly MH format.

Maildir libraries are widely available. For MH, you can use the nmh
tools.