In order to make the operation fast, when you delete a file, the operating system typically just sets a flag or removes an entry from a directory – the actual data within the file is left on disk until that space is needed, when it gets overwritten. Does the same apply to email messages?
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When deleted emails aren’t really deleted
In almost all email programs and web interfaces, deleting an email message doesn’t actually delete it. Instead, the message is simply moved to a special folder – typically called “trash” or “deleted items”. What happens next depends on the specific program or service.
Most online services automatically delete email from the trash after a certain amount of time – usually around 30 days. That gives you a month to change your mind and recover anything you didn’t mean to delete.
Desktop email programs often have a setting that controls what happens to the trash: either it’s left alone until you explicitly empty it, or it’s emptied automatically when you exit the program.
The real question is, what happens when deleted emails are actually deleted from the trash?
Online services: we just don’t know
When it comes to online services, we really don’t know how trash is handled. All of that is hidden behind the service provider’s interface. Chances are it varies from service to service, and in fact might even change over time; they’re not obligated to tell us.
The practical effect for users, though, is that once an email has been removed from an online service’s trash folder, it’s gone. There’s no getting it back – except for some exceptional circumstances I’ll talk about in a moment.
Desktop email programs: it varies
Desktop email programs store email on your computer in a variety of different ways. Some use a fairly complex database all kept in a single file, some use a slightly less complex separate database file for each folder, and others actually use your operating system’s disk structure, mapping email folders to disk folders and storing individual email messages as individual files.
As you might imagine, what happens when the trash gets emptied can vary a great deal.
Where the email program keeps individual messages as individual files, it’s pretty safe to assume that these behave exactly like deleted files, because they are deleted files. It’s possible that they could be undeleted.
Programs that use database files, like Outlook’s PST files, are much more complex. Much like a disk, when a message it deleted it’s simply marked as deleted, but not actually overwritten until the space it was using is needed. So, theoretically, deleted mail might still exist in one form or another within the database for some time.
Using a “compact” operation, when the email program provides it, typically removes the unused space, so the resulting database no longer has the message. The complication is that the compact function may itself operate by copying the database file to a new file and simply deleting the old one. That in turn means that there may be a deleted copy of the old database that could be undeleted, which could still contain remnants of the deleted message.
Told you it could get complicated.
Don’t forget about backups
One thing that’s very easy to overlook is the impact of backing up when it comes to retrieving email.
That exceptional circumstance I mentioned earlier is exactly that: your online email service could get a legal request to retrieve your email from their backups. That means that even if you have completely deleted an email, that service could possibly still recover it from the backups they took while the email was in your account.
The same is true for your own backups and your desktop email program. If you’re backing up as you should, it’s possible that an email you’ve completely deleted from your desktop email program could be recovered from one of your backups.
Don’t forget about the sender or recipient
Another scenario that people often forget is that email, by definition, starts off with two copies: the copy in the sender’s Sent Mail folder, and the copy that the recipient receives.
Regardless of which you are – sender or recipient – it’s always possible that the email message might be recovered from the other. Deleted emails can often come back to haunt you from this unexpected source.