Mail 2.0’s three different file types

One of the most significant changes in Tiger’s Apple Mail 2.0 was the shift from storing messages together in mbox files to storing them as individual emlx files. This is done primarily so that Spotlight could search your messages easily.

Each email is now stored as an XML document in a subfolder of your Mail folder.

However, if you take a peek inside your Mail folder, you will see that in fact Mail.app is using three different types of files to manage your messages. Some details about each type follow after the jump.

How are they different? Here are some guesses:

An emlx file is a pure plain text message. At the end of each file you will find some metadata including (for locally-cached IMAP messages) the original server-side mailbox and ID number of the message. MailTags also stores its metadata at the end of these files.

An emlxpart file is an attachment, either an image, a document or an HTML version of a message. It doesn’t contain the metadata which is included in an emlx file. Prior to Tiger, Mail.app stored attachments inside each mailboxe’s mbox file.

Now attachments are stripped off and stored separately as these emlxpart files with the same number as the corresponding emlx file. For example, a friend me a GIF file today. His message is locally cached in my Mail folder as 47803.emlx and the attachment as 47803.2.emlxpart.

As readers have pointed out in the comments, emlxpart files seem to occur only in IMAP accounts.

In IMAP accounts, a third type — partial.emlx — sometimes appears. I can’t work it out exactly, but I am guessing that this is a partially locally-cached copy of a message on the IMAP server, saved for indexing perhaps. If anyone knows better, I’d be glad to hear about it.

Tags: Apple Mail, emlx, mail.app, mbox

This entry was posted on Saturday, December 3rd, 2005 at 1:39 am and is filed under Apple Mail, Apple Mail Tips. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

8 Responses to “Mail 2.0’s three different file types”

mc says:

3 December 2005, 5:30 am at 5:30 am

Sorry to say, but perhpas this only shows up in IMAP contexts. I use POP because our FirstClass system is dumb dumb dumb as an IMAP system, and I have no such emlxpart files. I wish I did, sometimes…
Tim says:

3 December 2005, 11:46 am at 11:46 am

Very interesting.

I’ve just checked my one POP account – which I should have done before! I always forget that there are people who still use POP ;-) – and you’re absolutely right. Attachments are not stripped out of POP account emlx files, only IMAP ones.

Thanks for pointing that out.
John Speno says:

3 December 2005, 12:28 pm at 12:28 pm

partial.emlx could be a cached message minus attachments. Caching of attachments is an option, but it doesn’t have to be on. Just a guess.
Tim says:

3 December 2005, 1:01 pm at 1:01 pm

Hi John. I considered that. But wouldn’t all the messages in any given, cached folder be partial.emlx files? Why is it just some of them? That’s what puzzles me.
John Speno says:

4 December 2005, 5:12 am at 5:12 am

Is it just the messages that have attachments in that case?
Tim says:

4 December 2005, 9:44 am at 9:44 am

Doesn’t look like it to me, examining messages my own mail folders. What does examining yours reveal?
John Speno says:

6 December 2005, 12:17 am at 12:17 am

Sorry, I got nothing. It was just a guess and it sounds like a bad one. :-)
Hawk Wings » Blog Archive » What’s in your Mail folder? says:

6 December 2005, 11:22 pm at 11:22 pm

[...] You can read about the different emlx files Mail.app uses in another entry. [...]

Mail 2.0’s three different file types

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