1429012 - question: what is the difference between "compact" and "expunge" an IMAP folder in Thunderbird?

Status: RESOLVED INVALID

(Thunderbird :: Preferences, defect)

Description

[monperrus]

In the GUI and configuration options, two verbs are used "compact" and "expunge".

What is the difference between "compact" and "expunge" an IMAP folder in Thunderbird?

Comment 1

[Jorg K (CEST = GMT+2)]

Compact of a mailbox means that deleted or superseded messages are removed. For example, people save drafts and when a new version is saved, the previous version is superseded. When the final version is sent, the last saved version is also superseded. So people build up heaps of "dead" drafts in their Drafts folder.

When you (re)move a local message, it's not removed from the source folder, it's just marked superseded (or deleted). Compact gets rid of all those "dead" messages.

For IMAP accounts there is usually also a local copy in a mailbox somewhere, so also mailboxes associated with IMAP folders need compaction from time to time.

Expunging is telling the IMAP server to permanently remove a delete message from its message store. It might still hang around in a local mailbox copy.

As you know, IMAP has three deletion models: Mark as deleted, move to the trash folder, delete immediately. Expunging will get rid of messages marked as deleted.

In general terms: Compact is about cleaning up local folders and local copies of IMAP messages, Expunge is a server command.

Next time you have a question, ask on the [e-mail] mailing list.

Comment 2

[monperrus]

Thanks a lot Jorg for the super clear answer.

Comment 3

[monperrus]

> Next time you have a question, ask on the [e-mail] mailing list.

I posted the question here in order to have a clean URL, with a good <title> tag, well-indexed by robots (as done by stackoverflow). Would a message on [e-mail] have the same properties?

Comment 4

[Jorg K (CEST = GMT+2)]

Good question, that mailing list has archives https://groups.google.com/forum/#!forum/mozilla.dev.apps.thunderbird but I don't know how well they are indexed.

Comment 5

[monperrus]

> As you know, IMAP has three deletion models

Thanks for clarifying this. Thanks to you and some additional UI experiments, I have just understood all options! It seems I have been completely misled by "remove immediately" for years. 

So, here is an UI improvement suggestion: bug 1429201

Comment 6

[monperrus]

In the main configuration page of the IMAP account ("Server settings"), there is under "Message storage", the option "Clean up ("Expunge") Inbox on exit".

Does it do:
- a local storage compact AND and an IMAP expunge?
- only a local compact?
- only an IMAP expunge?

Comment 7

[Jorg K (CEST = GMT+2)]

No compact. So only IMAP expunge.