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Question about compacting folders

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  • Last reply by Matt

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Today, in Thunderbird, I received the notification that I should compact my folders. I was about to go and turn off these reminders without compacting the folders -- which is what I did on my last computer. Then I read in some thread that it's actually an "important" thing to do, which seemed to contradict something I read about it at some point in the past. There was one thread from at least a couple years ago, probably several years ago (I wish I could find the thread), but somebody had "compacted" their folders, which then caused something to happen that they didn't expect to happen -- I can't remember what -- but I think it was something along the lines of, they lost something they could never get back. I don't know if they lost some messages that they wanted, I don't know. But this person was suggesting that there should be a warning about "this" happening when you compact the folders. Then someone else wrote a very long and very well-reasoned reply explaining why expecting such a warning wouldn't really make much sense or be necessary, because the possibility of "this" happening was so obvious that a warning wouldn't be warranted.

So I figured, if "compacting" folders can make me permanently lose something I don't want to lose, then it's something I don't want to do. (Again, if I could find that thread, I would post a link and/or provide more details).

Then in another thread I read today, it was suggested that it's riskier not to compact your folders. So which is it? Why is it that someone had some problem (again, I'm sorry, I wish I could find the original thread) where they lost something permanently when they did compact their folders, and others are saying it's riskier not to?

Modified by michael.26.murrin

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You could just as well ask why the guy with the 20 2X4 on the roof of his sedan had an issue with the police in the way home from walmart.

Compacting is essential for two reasons as far as I am concerned. But first consider exactly how this compact works. Thunderbird marks mail in a folder deleted when you delete it and makes a copy in the deleted folder. there a good technical reasons to do this, but it is counter intuitive to what most people think happens around moving things to folders. Thunderbird also does this when moving mail from the inbox to any other folder. So the deleted message is still there in the file for that folder permanently. Compacting actually removes these "marked as deleted" emails from the folder by copying all of the "current" emails in the folder to a new file with an NSTMP## name and deleting the old file when the compact is completed. So if the compact fails, there is an NSTMP folder appears in local folders.

So why is it essential?

  • One is to actually get rid of deleted mail. Because of the "mark as deleted" process, mail that you deleted on that hard disk is still available to those that know how to undelete. It is not very technical either given the storage is a plain text file. It might be very embarrassing to have email from 5 years ago surface in some circumstances.
  • Unidentified malware is removed. ANti virus program are only as good as their definition database, so when a full disk scan occurs down the track. Old malware that never did anything is often identified and the entire folder of mail is deleted or quarantined. Having compacted the folder that mail would no longer exist to be identified.

Most of the issues I have seen oven the past 8 or 9 years are because people rely entirely on their anti virus program to identify and clean supposed infections. They do that by removing the files this apparent malware is contained in. Thunderbird uses an index file to load the message lists and this is not updated correctly when the anti virus unilaterally deletes the actual message file. SO when compact occurs and a full reindex occurs it is a case of oops I lost all my messages before XXXXX date. The message in many cases have been gone months or even years, but the loss was not apparent until the compact. Yet another reason or regular compacts so if something like that happens you stand a chance of undoing what the anti virus did.

A side effect is that the space those mails occupied is released. That was very important in it's own right when people had hard disk storage measured in the megabytes.


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