How to Delete a Stuck Outbox Email That Freezes Apple Mail on macOS Tahoe

A huge attachment can leave Apple Mail in a bad loop on macOS Tahoe. The message sits in Outbox, Mail keeps trying to process it, memory usage climbs, and the app freezes before you have enough time to delete the message normally. Taking the Mac offline may stop the send attempt, but in some cases the message returns as soon as Mail is reopened.

This happened in a recent macOS Tahoe 26.6.2 case after a roughly 30 GB file was attached to an outgoing message. The message never appeared in webmail because it was still stored in Mail’s local Outbox. The successful fix was to quit Mail and remove the stuck Outbox data under the user’s Mail library.

On Tahoe, the relevant Mail store is commonly under:

~/Library/Mail/V10/

The exact Outbox path varies because Mail uses opaque account and mailbox folder names. A typical path eventually leads to:

~/Library/Mail/V10/.../Outbox.mbox/.../Data

The safest way to deal with it is to keep Mail offline, close Mail completely, find the correct Outbox, move its data somewhere safe, and only delete that backup after Mail is working again.

Note: V10 is the name of Mail’s on-disk data store used on current macOS versions. It is not the version number shown for the Mail application itself.

Try the normal Outbox deletion once

If Mail stays responsive for long enough, try the simple route before touching its files.

Disconnect Wi-Fi and Ethernet.
Open Mail.
Select Outbox under “On My Mac” or the affected account.
Select the stuck message and delete it.
Quit Mail normally with Command-Q.
Reopen Mail while still offline and check whether the message is gone.

If the message comes back, Mail freezes before the deletion finishes, or the app runs out of memory again, stop reopening Mail and use the filesystem method below.

Before editing the Mail library

Mail’s Library folder contains real mailbox data. A mistake here can affect other mail stored locally, especially messages under “On My Mac.”

Make a Time Machine backup if one is available. Apple states that Time Machine backs up email along with other user files. At minimum, keep a copy of the Outbox you are about to change.

With an extremely large attachment, duplicating the whole Outbox may require more free disk space than the Mac has. In that situation, moving the problem files to a temporary folder on the same disk is a practical alternative. Do not empty the Trash or delete the temporary copy until Mail has opened normally and your other mailboxes look correct.

Step 1: Disconnect the Mac from the network

Turn off Wi-Fi and disconnect Ethernet before opening Mail again.

This prevents Mail from retrying the outgoing message while you work. It also removes the chance that a partially processed message suddenly leaves the Mac while you are trying to clean up the queue.

Leave the Mac offline until the stuck message has disappeared from Mail.

Step 2: Quit Mail completely

If Mail is still responsive, press Command-Q.

If it has frozen, press Option-Command-Esc, select Mail, and choose Force Quit.

Do not change files inside Mail’s data store while Mail is actively using them. A normal quit is preferable when possible because the app can finish writing its current state. Force Quit is appropriate when Mail no longer responds.

Step 3: Open the Tahoe Mail data folder

In Finder:

Click Go in the menu bar.
Choose Go to Folder.
Enter:

~/Library/Mail

Open V10 if it is present.

The V10 directory can contain folders with long UUID-style names rather than recognizable email account names. That makes manual browsing confusing, especially when several accounts are configured.

Do not delete the V10 folder itself. It contains far more than the stuck Outbox.

An easier way to find every Outbox with Terminal

Terminal can locate the Outbox folders without requiring you to guess which UUID belongs to which account.

Open Terminal and run:

find "$HOME/Library/Mail/V10" -type d -name "Outbox.mbox" -print

If you want to avoid assuming the store is V10, use:

find "$HOME/Library/Mail" -type d -name "Outbox.mbox" -print

You may get more than one result. That is normal when Mail has multiple accounts or local stores.

To compare their sizes, run:

find "$HOME/Library/Mail/V10" -type d -name "Outbox.mbox" -exec du -sh {} \;

An Outbox containing a huge attachment should usually stand out by size.

If Terminal says “Operation not permitted”

macOS protects Mail data with its privacy controls. Go to System Settings > Privacy & Security > Full Disk Access and allow Terminal access, then quit and reopen Terminal before trying the command again.

Apple describes Full Disk Access as permission to access files from other apps, including Mail. There is no need to disable System Integrity Protection for this task.

Step 4: Back up or quarantine the affected Outbox

Once you have found the suspicious Outbox.mbox, open it in Finder. The internal structure can contain one or more additional opaque folders before you reach Data.

The Tahoe case that prompted this guide was fixed by clearing the contents under the affected Outbox.mbox/Data area.

Before doing that, preserve what is there.

If disk space allows, copy the affected Outbox.mbox to an external drive or another safe location.

If copying tens of gigabytes is impractical, create a temporary folder such as Mail Outbox Backup on the Desktop and move the contents of the affected Data directory into it while Mail is closed. A move on the same disk normally avoids creating another full copy of the huge attachment.

This also gives you a way back if you discover that another unsent message was stored in the same Outbox.

Step 5: Remove the stuck Outbox data

With Mail closed and the Mac still offline, clear the contents of the Data directory inside the affected Outbox.mbox.

Do not remove neighboring account folders, MailData, Inbox mailboxes, Sent mailboxes, or the entire V10 folder.

Clearing the whole Outbox data area can remove other unsent messages queued in that same local Outbox. If there are messages you need to keep, preserve the Outbox first and avoid permanently deleting the backup until you have checked it.

For the reported Tahoe 26.6.2 problem, clearing the affected Outbox data removed the oversized message and allowed Mail to open normally again.

Can you delete only the giant message instead?

Sometimes, but it is harder to give a safe universal file path for one message because Mail’s internal layout can split message data and attachments across nested folders.

Advanced users can inspect the affected Outbox and look for abnormally large or recently modified files. This command lists the largest files near the end of the output:

find "/full/path/to/Outbox.mbox" -type f -exec du -h {} \; | sort -h | tail -20

Replace /full/path/to/Outbox.mbox with the path you found earlier.

If one file clearly accounts for most of the Outbox size, moving that file to a temporary folder may be enough. The association between a message record and its attachment files is not always obvious, so clearing the affected Outbox’s Data contents is more predictable when the Outbox contains only the failed message.

Step 6: Reopen Mail while still offline

Open Mail before reconnecting Wi-Fi or Ethernet.

Check the following:

The oversized message no longer appears in Outbox.
Mail stays open without the memory warning.
Inbox, Sent, Drafts, and any “On My Mac” mailboxes you use still appear normally.

If everything looks right, reconnect to the network. Send yourself a small plain-text test email before trying another attachment.

Keep the Outbox backup for a little longer. Once the test message sends and Mail remains stable, you can delete the quarantined data to reclaim the storage space.

If Mail restores the bad window when you open it

macOS can reopen windows that were present when an app last quit. Apple documents a simple one-time way to prevent that: hold Shift while opening the app.

Quit or force quit Mail, then hold Shift while launching Mail again. This tells macOS not to restore the windows that were open during the previous Mail session.

This can buy enough time to inspect the Outbox after the file cleanup, especially if Mail keeps reopening the same compose or message window.

Is Safe Mode required?

No evidence shows that Safe Mode is required for the Outbox file removal itself. The successful Tahoe report used Safe Mode during the cleanup, but the user also indicated that it might not have been necessary.

Apple describes Safe Mode as a diagnostic startup method that helps isolate problems caused by software loaded during startup. It can still be useful here when Mail or related startup behavior keeps interfering with the cleanup.

On an Apple silicon Mac:

Shut down the Mac.
Hold the power button until startup options appear.
Select the startup volume.
Hold Shift and click Continue in Safe Mode.

On an Intel Mac, restart and hold Shift until the login window appears.

Once in Safe Mode, keep Mail closed, perform the Outbox cleanup, restart normally, and test Mail offline first.

What if the message is gone from disk but Mail still shows it?

Apple notes that changes made to mailboxes through Finder may not immediately appear inside Mail. If the stuck message has been removed from the filesystem but Mail still shows a ghost entry or incorrect Outbox count, rebuild the mailbox before touching Mail’s global index files.

When Mail is stable enough to use:

Select the affected mailbox in the sidebar.
Choose Mailbox > Rebuild.
Allow Mail to finish updating the mailbox list.

Rebuild is an Apple-supported command for refreshing the list of messages in a mailbox.

Last resort: rebuild Mail’s Envelope Index

If the actual Outbox data is gone but Mail still has stale message records, counts, or repeated display problems, Mail’s Envelope Index may need rebuilding.

Do this only after backing up your Mail data. Rebuilding the index affects Mail globally and can take time on a large mailbox collection.

Quit Mail, then go to:

~/Library/Mail/V10/MailData

Look for files named:

Envelope Index
Envelope Index-shm
Envelope Index-wal

Move those files to a temporary backup folder rather than deleting them immediately. Reopen Mail and allow it to rebuild its index.

This step is widely used for damaged Mail indexes, including Tahoe-era reports, but it should stay behind the targeted Outbox cleanup. Removing the oversized message from Outbox.mbox addresses the source of this specific freeze. Rebuilding Envelope Index deals with Mail’s cached view of the mailbox afterward.

What not to delete

Avoid broad cleanup advice that tells you to erase all of ~/Library/Mail/V10, delete every account, or remove random files under Mail’s container folders.

For this problem, keep the scope narrow. The affected Outbox.mbox is the target.

Also avoid treating this folder as the Outbox:

~/Library/Containers/com.apple.mail/Data/Library/Mail Downloads

Mail Downloads is used for local copies of attachments that you open from messages. Clearing it is a different storage cleanup task and does not directly remove a queued message from the local Outbox.

Why the message does not appear in webmail

Apple distinguishes mailboxes stored “On My Mac” from mailboxes stored on a mail server. An “On My Mac” mailbox is local to that Mac.

A message that is still stuck in a local Outbox may never have reached the provider’s SMTP service or server-side mailbox. Webmail therefore has nothing to delete. The Mac’s local Mail store has to be fixed first.

This is also a useful diagnostic clue. If the message is absent from webmail but present under “On My Mac” and Mail freezes while processing it, local Outbox data deserves attention before you reset the email account or change server settings.

A 30 GB file is too large for Mail Drop too

Apple Mail can use Mail Drop for attachments that exceed a provider’s normal message limit, but Apple currently limits Mail Drop attachments to 5 GB.

A 30 GB file is therefore outside Mail Drop’s supported size as well. Use a file-sharing service, cloud drive, NAS link, or another transfer method designed for files of that size. Send the recipient a download link instead of attaching the file directly to an email.

If the Outbox folder is missing

First confirm that Mail is fully quit, then search the entire Mail directory instead of assuming a particular account folder:

find "$HOME/Library/Mail" -type d -name "Outbox.mbox" -print

If no Outbox exists and the message still appears in Mail, the problem may have shifted from stored message data to Mail’s index or restored application state. Try the Shift-launch method, then Mailbox > Rebuild if Mail opens. The Envelope Index reset belongs after those steps.

If the message also appears in webmail, handle it at the provider side first because that indicates the message or queue is no longer purely local.

If there are several Outbox.mbox folders

Do not clear them all.

Compare their sizes with du -sh, inspect modification times in Finder, and identify the one that grew when the oversized message was created. A 30 GB attachment gives you a useful clue because the affected Outbox may be dramatically larger than the others.

When the size difference is unclear, back up each candidate before changing anything and work on one Outbox at a time.

Why deleting the message in Mail can fail to stick

Deleting a message through Mail’s interface still requires Mail to update its local mailbox data and indexes. If the app runs out of memory or is force-quit before that update finishes, the deletion may never be committed. The same queued message is then available again the next time Mail opens and processing starts over.

Filesystem cleanup works around that loop by removing the local queued data while Mail is not running.

The safest order to follow

For a stuck oversized Outbox message on macOS Tahoe, start offline and try the normal delete once. If Mail freezes or the message returns, quit Mail and remove the affected Outbox.mbox data while keeping a backup. Reopen Mail offline, test it, then reconnect.

Use Shift-launch or Safe Mode when Mail keeps restoring the problem state. Use Mailbox > Rebuild for a stale mailbox view. Rebuild Envelope Index only when the message data has already been removed and Mail still shows bad index information.

I recommend keeping the quarantined Outbox data until you have reopened Mail, checked your local mailboxes, and successfully sent a small test message. Once those checks pass, delete the backup copy and empty the Trash if you want the disk space back.