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What Does It Mean When My Email Program Asks If It Should Compact My Email?

Question: When I close my email program, Windows Mail, I constantly get a message that says I can compact the mail. Do I wish to do that? I say no as I don’t know what compacting it entails. What happens when it’s compacted and will I be able to reconstitute the mail that I have in the various folders so that I may respond to it, forward it, or whatever?

Compacting should make the files on disk smaller and potentially the access of emails thereafter a little faster.

I say ‘should’ because compaction has what I’ll call a sordid history. In Outlook Express, compaction was a land mine.

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Outlook Express couldn’t handle a couple of situations, such as really large email folders. Some people would click Yes to compact their files and half of their email would disappear. That’s not supposed to happen.

As a result it’s one of several reasons I recommend leaving Outlook Express behind.

I haven’t heard of it happening with Windows Mail, Windows Live Mail or Outlook, which all use completely different storage technologies.

So what does it mean? Why do we need to compact in the first place?

Compaction is all about file space

When you delete a file, your machine doesn’t remove the file, but simply marks the space as free.

With email, the same thing happens. When you delete a message, your email program moves it to your trash folder. Then when you empty that, the message is marked as being deleted. It’s not physically removed, you just don’t see it any more.

After you’ve emptied your trash, the message could theoretically still be there taking space (even though you would need special tools to even try to recover it).

Now, if this happens over a long period of time (say you’ve received a gigabyte of email, but you’re only keeping 100 MB of it), that means there could be as much as 900 MB of email that you’ve deleted still taking up space on your hard disk and in your email folders.

When you compact, all of your permanently deleted email gets deleted for real. The files are rewritten so they only contain the mail that you actually have. As a result, the mail has a smaller file size and it becomes slightly faster to access because the messages are closer together. That’s all that compaction really does.

Should I compact?

Binary DataIf you’re at all unsure or scared about compaction, backup first.

Just take an image backup of your system. Hopefully, you’re doing that already. Then fire up Windows Mail and let it compact. Once it’s done, poke around and see if anything is missing. I’m certain that nothing will be. And if nothing is, then you’re done.

If something is missing or goes disastrously wrong, then restore your machine from the backup. But I don’t believe that’s going to happen unless you’re running Outlook Express.

Compacting and Outlook Express

Now, I honestly believe that if you’re running Outlook Express, you really need to consider using a different email program. The issues that I’m covering here with respect to compacting are only the tip of the iceberg. And Outlook Express is no longer being supported by Microsoft, so the issues will never be fixed.

If Outlook Express ever asks you to compact, don’t. The compact message may appear a lot – this is another bug in Outlook Express. You could compact one day and the application would ask you to compact the next even though it doesn’t need it.

Like I said, these are issues with Outlook Express. They’re not going to get fixed, so just don’t compact if you’re running Outlook Express. It’s simply too risky. I’d rather recommend that you move to a different email program like Windows Mail, Windows Live Mail, Thunderbird, Outlook, or going online with something like Gmail. Almost anything other than Outlook Express is a much safer approach to preserving your email.

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7 comments on “What Does It Mean When My Email Program Asks If It Should Compact My Email?”

  1. Mozilla Thunderbird also recommends compacting too, Actually, I think Mozilla Thunderbird stores the email in the mbox format, though I don’t know how Outlook stores theirs.

  2. One way to back up your emails is to add an IMAP account to your email program. This would be an IMAP version of the same account you are using. Then copy the emails from your POP3 version of that account to the IMAP inbox and send mail folders. This will cause your email program to upload all of your emails back to the server of your email provider. Then you can install a new email program or use a web interface to access and/or download your emails. I suggest sticking with IMAP with your new email program as it keeps your emails always backed up. I tested this out with Outlook Express and it worked well.

  3. The problem for me is, I do use Windows mail, but I can’t for the life of me work out how to compact messages. It does not ask me when I exit; how can I make it ask me? I’m using Windows 8, which as you know is this really “brilliant” program that has no “tools” and even when you go to “options” there is no “advanced” etc etc.

  4. Thunderbird keeps telling me I can save disc space by compacting — and the amount of saved disc space grows after I delete even thousands of old emails.
    If I’m going to compact, I want to make sure I don’t lose any emails saved — either in my inbox or in trash. They serve as my personal archive.
    How do I make sure I only get rid of already deleted emails? And can I do this one email address at a time?

    (I have Carbonite as a back-up, and over 300 GB of unused disc space on my computer. The amount I can “save” is currently up to 3.9 GB)


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