Maildir
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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. Multiple incompatible methods!!!
- 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
- Each file is a self-contained valid RFC822 message datastream
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
Nemo sez =
Arbitrary unfriendless is anathema to me.
So...
How to fix the cons of maildir?
Information in 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.
- What is the date based on? Envelope date or message date? In mbox, envelope date is encoded in the From_ line. In maildir it is the datestamp of the file? Or is it forgotten?
Links
- http://wiki.dovecot.org/MailboxFormat/Maildir - dovecot issues with maildir
- http://www.inter7.com/courierimap/README.maildirquota.html - courier's maildir++ implementation
- http://qmail.org/qmail-manual-html/man5/mbox.html - qmail's doc on the mbox format
- http://homepages.tesco.net./~J.deBoynePollard/FGA/mail-mbox-formats.html - "mbox" is a family of several mutually incompatible mailbox formats.
