recommended storage format for email messages?

[perl5ever]

Hi fellow Monks!

I am storing email messages I get from an IMAP server into files, and because of their small size and to save on disk space I want to store multiple messages (like 100's) in a single file.

I'm looking for a good storage format to use, i.e. one that allows for efficient and reliable parsing. The messages will not be used with a mail reader, so there is no need to use any 'mailbox' formats.

The storage format only needs to be efficient for sequential traversal, and, of course, it would be nice if there was a perl module which already implemented the format. Having it be a 'plain text' format (so one can use command line tools like 'grep') would be a bonus, too.

Any suggestions?

[davorg]

Well, mbox is a pretty simple plain text format for storing mail. I know that you don't have a need for "mailbox" formats, but I can't think of a simpler way to store mail messages.

It ticks your other boxes too. You can use grep on in and there are Perl modules for dealing with it too.

[afoken]

I use IMAPdir, which extends Maildir++ with a folder hierarchie. Maildir++ inherits from maildir and adds a quota system. All of these give you one file per e-mail, all without needing locks, NFS-safe, and without any modification to the e-mail. You can parse the files with exactly the same tools that you use to parse an e-mail fetched from the net. And yes, you can use grep and all other text processing tools on the files in the maildir/Maildir++/IMAPdir folders. Sequencial access is no problem, just use readdir() or File::Find to iterate over the directory.

Storing several hundred files in an ext3 filesystem is no problem. With 100_000 files, things begin to look different. It works, but ext3 does not like it and slows down. RaiserFS is said to be faster in that case, but I've never tested it.

I've used the de-facto standard mbox format since the days of Netscape Communicator, but it became slow as hell when the mailboxes filled up. Some day, I gave the IMAPdir format a try, splitted all mailboxes into the IMAPdir format, switched my IMAP daemon from pine's to bincimap, and found that it was much faster.

Alexander

[JavaFan]

Well, I was going to suggest the 'mbox' format - which is 'plain text', and has a battery of Perl modules able to parse it, but it seems you want to dismiss that format.

[perl5ever]

The main reason I don't like the mbox format is that it does not support an efficient way to skip over messages in the file.

All I'm looking for is a storage format that is line-based and has a header before each message indicating the message's size.

I could invent such a format, but I was wondering if one already existed.

[jhourcle]

Sounds like you just need to generate an index, then, with the starting line of each of the messages. If you kept it separate, then normal mbox-reading programs could use it, and you'd have your alternate way of skipping to messages.

[hangon]

A quick and dirty method I've used is to add a fixed length ascii field before each message. The field contains the message length in bytes. Then concat the messages with length field into a single file. To traverse, use read to get the message length, then read to grab the entire message or seek to the next one. The format is fairly trivial to code as long as your file will be used readonly. Note that it may not be portable to a different OS.

     1148
Return-Path: <[e-mail]>
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Subject: file format
Date: Tue, 14 Jul 2009 16:00:18 -0400

email message body bla bla bla
etc ...
etc ...
etc ...

      729
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Received: ...
Date: Tue, 14 Jul 2009 16:00:18 -0400

another email bla bla bla
etc ...

[Bloodnok]

Your requirement that ...there is no need to use any 'mailbox' formats... is, AFAIK, of no consequence since the single file storage format is a function of sendmail - mail readers know that the e-mails in the mailbox file are stored as sequential ASCII text blocks - at least on *NIX anyway.

I don't know and care less about the format used by Lookout (errrm, Outlook)/Exchange - but I dare bet it's in some weird proprietary binary format...