File formats

What Deleting an Email Actually Does

Almost every surprise here comes from somebody believing they did the fifth step when they did the second.

Robert Smith 7 September 2026 6 min read

Deleting an email is five different operations sharing one word. Delete means five different things and they all wear the same word. Moving a message to another folder. Removing it from that folder. Removing it from a server. Removing it from a file. Finally reclaiming the space. Which one you performed decides whether the message is still there. Most of the time it is.

This matters when somebody asks whether a mailbox has been cleared. The honest answer is a question about which layer they mean.

The Five Layers of Deleting an Email

Pressing delete once starts at the top of this list and rarely gets past the second line.

Moved To a folder called deleted or trashThe message has not left anything. It is in a different folder and still fully searchable
Removed from the folder Emptying that folderGone from the list. Whether it has left the file is a separate question with a separate answer
Removed from the server Only where the account is connectedUnder IMAP this happens with step two. A POP account leaves the server untouched
Removed from the file Depends entirely on the formatSome formats delete a file. Others mark space as reusable and change nothing else
Space reclaimed A separate operation nobody runsCalled compacting in Outlook. Until it happens the message sits inside the store, findable by anything reading the format directly

Almost every surprise in this area comes from somebody believing they did the fifth when they did the second. The two look identical from inside a mail program.

What the Mail Format Decides About Deleting

Step four behaves completely differently depending on where the mail is stored. The difference is structural rather than a setting.

Format	What deleting one message does
PST and OST	Marks the space reusable. The file does not shrink and it stays in it
MBOX	Marks it. The file only changes when something rewrites the whole thing
Maildir	Deletes one file. The only format here where deleting means deleting
EML on disk	Deletes one file, subject to whatever the operating system does next
A server mailbox	Depends on the provider, usually a retention window of days

This is why a mail file never gets smaller when you clear it out. Delete a thousand messages from a four gigabyte personal store and you still have one. The space is available for new mail and the old mail is still inside, which anything reading the file format directly can see.

The Protocol Half of What Deleting Does

Where the mail is connected to an account, the protocol decides how far a deletion travels.

Under IMAP

It travels

delete on the phone
  server updated
  laptop updated
  tablet updated

seconds, everywhere

Synchronisation working correctly. There is no local copy to fall back on, because none of them was ever independent.

Under POP

It does not

delete on the laptop
  server unchanged
  other machines
  unchanged

one machine only

Which is why a mailbox somebody emptied years ago is often still full when they finally sign in to webmail.

Neither is safer. One makes a deletion complete and irreversible everywhere at once. The other leaves copies nobody remembers, which helps until somebody wanted the message actually gone.

Removing an attachment is the sharp version of this. In a connected mailbox that is a change to the message rather than a change to your view of it, so the removal reaches the server and every device. People do it to save space and discover later that the file is gone from the only copy there was.

The Copies Deleting an Email Never Touches

Even a deletion that completes all five steps leaves everything made before it.

Copy	Affected by your deletion
A backup taken last night	No. Still holds the message
An export made in 2019	No. Nobody remembers it exists either
The recipient's mailbox	No. It was always their copy
Server side archiving or journaling	No. Often the whole point of it
A colleague you copied in	No

Deleting removes one copy of something that was never in one place. That is worth knowing in both directions, since it is either a relief or a problem depending on why you are asking.

Backup rotation is what eventually removes it. A message deleted today disappears from the backups when the rotation reaches those copies rather than when you deleted it, which is a matter of weeks. Nothing you do in a mail program affects that timing.

Removing an Email Properly

Clear the deleted items folder. Steps one and two. Everything most people do stops here. The store still holds the message.
Compact or rewrite the store. Outlook calls it compacting. Until this runs the message is inside the file and anything reading the format can find it.
Deal with the copies made earlier. Backups, exports, the archive on a drive somebody made once. This step is always missed and it decides the answer.
Check the server separately. A POP account leaves everything behind. Signing in to webmail is the only way to see what is actually there.
Write down what you did. Where a deletion has to be demonstrable rather than merely done, the record is half the work.

Nothing here is advice about a legal obligation. Where a retention rule or a hold applies, that instruction governs and this page does not. Deleting during a matter is a different subject and a serious one.

Where the question is what a file still contains rather than what a mail program shows, only reading the file directly settles it. Our file viewers open a store in a browser tab and show what is in it, which is not always what the mailbox listed.

Behaviour checked against the referenced articles and vendor documentation in August 2026. Retention windows vary by provider and by plan, so treat any figure as a starting point rather than a guarantee.

Questions People Ask

7 questions, answered in full below.

Where does a deleted email actually go?

Usually to another folder, which is why it is still findable. Emptying that folder is the second step and it removes it from the list. Whether the bytes have gone anywhere at that point depends entirely on which format the mail is stored in.

Why has my PST not got smaller?

Because deleting marks space as reusable rather than removing anything. The file only shrinks when something rewrites it, which Outlook calls compacting. Until then the messages are still inside and the size on disk is unchanged.

Does deleting on my phone delete everywhere?

Under IMAP yes, within seconds, because every device shows the same server folder. Under POP no, because each machine holds its own copy. Which one you have was decided when the account was set up.

Is a deleted message gone from backups?

No. This is where people are most often surprised. A backup taken before the deletion still holds the message. It stays there until the backup rotation reaches that copy. Deleting from a mailbox does nothing to any copy made earlier.

What does removing an attachment do?

More than it looks. In a connected mailbox the removal edits the message itself, so it travels to the server and out to every other device. What you removed was the only copy, not your local view of one.

Can deleted mail be required in a legal case?

What exists can be required. Where it exists is the question. Server retention, backups, an old export, another recipient

How do I remove mail so it is genuinely gone?

Empty the deleted items folder, then compact or rewrite the file so the space is reclaimed, then deal with every backup and export that predates the deletion. The third step is the one that gets missed and it is the one that matters.

Sources

Where the figures and behaviour described above were checked.

Data erasure Wikipedia
Internet Message Access Protocol Wikipedia
Maildir Wikipedia