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What is compacting folders in Thunderbird, and why you should do it


Are your Thunderbird folders taking up a lot of disk space, even though you only have a few messages? Is Thunderbird slow to open folders? It’s probably because you have not compacted your folders.

When you delete a message, it doesn’t really get deleted from the folder. It gets marked as deleted. Thunderbird sees that marking, and knows not to display the message. Compacting a folder will command Thunderbird to remove all messages marked as deleted from that folder.

To compact your folders, go to the File menu and select Compact Folders.
To compact an individual folder, right-click on the folder and select Compact.

If you’re having any issues, post in the Thunderbird Support forum at


One commentcomments13

  1. Does this apply to both POP and IMAP accounts?

  2. Why does this not happen automatically in some manner?

    Users should not *need* to know something like this. It should just work.

  3. Mahesh,
    It applies to POP and local storage of IMAP.

    I don’t know. It’s one thing I’ve been pushing for a long time.

  4. I presume this compaction function is by the SQLite program part of the Mozilla product running the VACUUM command. I have seen web posts about using the VACUUM command for Firefox profiles, out of the Error Console, which seems in some cases to be posted online with a truncated command to cut/paste. I have seen compacting described as doable via the VACUUM command from the SQLite Manager addon, for any Mozilla *.sql file you can get to in a database loaded into the addon. I am inexpert about SQLite, but I could load a profile database into that addon to see individual *.sql entries.

    For Firefox there is a freeware (but not open source) utility, speedyfox, which I have used without problem fore easy profile-by-profile cleaning – not file by file. It has an icon and interface listing of profiles comparable to J.Griffin’s Profile Manager stand-alone program. I left a comment on his blog too, about it, and whether that functionality added to his utility as open source was a promising project.

    Firefox does not have the compacting file menu entry, not that I could find on any of the version menu displays I checked, and I read somewhere on the web that newer releases do it automatically. I have no idea whether this is so, nor did I save a link where the claim’s been made.

    If you are unfamiliar with the speedyfox utility, a Google will get info. Again I have used it on my profile w/o any mishap, no file corruption, etc., and it seemed to make things faster.

  5. eric z,
    This has nothing to do with sqlite files. The files being compacted are UNIX mbox files.

  6. Can you still search folders or emails that have been compacted?

  7. Can you still search folders or emails that have been compacted?
    I have the same question.
    Thunderbird kept asking me if I want to compact my files while in inbox.
    I clicked on ok,then all my inbox e-mails disappeared and I cannot find them.
    It is like it just deleted my entire inbox.Everything else stayed.
    Thanks for any help

  8. same issue – compacted the inbox, all the files disappeared. Why? Where did they go? can they be recovered?

  9. If files messages disappeared, you might be able to get them back by doing this:
    Right-click on the folder, and click Properties.
    Click Repair Folder.

  10. Now I am afraid to do it in case I lose all my messages! John G – were you able to get them back using the Repair Folder option?

  11. Compacting folders does not delete all messages. If John G is having a problem viewing messages after compacting, he can email me or better yet, post in the Thunderbird Support forum at

  12. The last I know, for newsgroups posts, deleting messages was still confused with cancelling them, and you could not delete a newsgroup message without cancelling it first (and as part of the same command). Has this been corrected?

  13. When I clock compact then the whole inbox disappears. The rest remains the same but all my inbox messages are gone… Help !