Maildir

Revision as of 10:15, 30 March 2009

Maildir is a popular alternative to the almost ubiquitous mbox format (formats - see below). However, I have some issues with it...

First though, let's look at mbox

mbox

Where each folder is a file, and each message is a segment within that file

Pro

• Easy to grep from the commandline (grep STRING file)
• Easy to search within folder using 'less' or similar
• Faster to open as only one fopen required

Con

• Requires $From escaping
• Requires file locking for multiple access handling (esp nfs?)
• Slower to write changes as whole mbox needs re-writing

maildir

Where each folder is a directory, and each message is a file in that directory structure

Pro

• Multiple simultaneous access
• No need for escaping anything
• Changing status on an individual message is VERY fast (file rename only)
  • Can also be done from the commandline easily

Con

• May not be able to search from commandline so easily with multiple ('rgrep STRING maildir/' may return MULTIPLE files, which is then harder to search through with 'less', etc)
• Filename uniqueness is arbitarily unfriendly to human readability

So...

How to fix the cons of maildir?

Filename

The standard says that the name shoulnd't be of care to the MUA, so let's make it at least human useful. What is wrong with:

• YYYYMMDDHHMMSS.SubjectLineUpTo40CharsLong.md5:2,

This provides human readable date, and messages are then likely sortable by date from commandline easily. Date plus "." = 15 chars. Then let's have up to 40characters of subject line - this should allow for reasonable hinting as to message contents from the filename. That's 55 characters used so far. The first 4 characters of an md5sum of the message itself should be a final uniqueness check (if it is identical to all the others then we have a problem! That brings us to 60 characters (the seperating period making the shortfall for those keeping count). And at the end let's say that status chars (including ":2,") could grow to 10 chars. That's 70 chars which means a basic 'ls' stays comfortably inside a standard 80column terminal.

Links

• http://wiki.dovecot.org/MailboxFormat/Maildir - dovecot issues with maildir
• http://www.inter7.com/courierimap/README.maildirquota.html - courier's maildir++ implementation
• http://homepages.tesco.net./~J.deBoynePollard/FGA/mail-mbox-formats.html - "mbox" is a family of several mutually incompatible mailbox formats.