Outlook Email Stuck in Outbox: Every Fix, in Order

Outlook email stuck in Outbox is one of those problems that looks simple — the message is right there, you can see it, it's just not going anywhere — but the fix isn't the same every time, and the most common thing people try first (opening the message from the Outbox) can actually make it worse. The right sequence depends on which of several possible causes you actually have.

The Outbox is a holding folder by design. Every email you send sits there while Outlook packages and transmits it to your mail server. Under normal conditions, the message moves from Outbox to Sent Items in a few seconds. When something interrupts that handoff — a connectivity mode, a size limit, an antivirus scanner, a broken authentication token, or a corrupted data file — the message stays put, and Outlook usually does a poor job of explaining exactly why.

This guide covers every cause that produces a stuck Outbox message in Outlook, on both the new Outlook and classic desktop Outlook on Windows, with a separate note for Mac. The fixes are ordered from the one that changes the least to the one that involves rebuilding something. Work through them in sequence rather than jumping to the nuclear option — most cases never make it past the second step.

Why is an Outlook email stuck in the Outbox?#

There are seven distinct causes, and treating the wrong one wastes time or breaks other things. The table below matches each cause to its quick confirmation test so you can identify what you actually have before touching any settings.

Fix 1: Turn off Work Offline mode#

This is the most common cause of a stuck Outbox message and the most commonly missed because Work Offline is easy to enable by accident — it's a single click in the Send / Receive tab, and nothing alerts you when it's on except the status bar text at the bottom of the window. If Outlook says "Working Offline" anywhere in the interface, this is almost certainly your cause, and fixing it takes ten seconds.

1. 1

   Look at the status bar

   Glance at the bottom of the Outlook window. If it reads "Working Offline" or "Disconnected," Work Offline mode is on or Outlook has lost its connection to the server.

2. 2

   Open the Send / Receive tab

   In the Outlook ribbon, click the Send / Receive tab. Look for the Work Offline button on the right side of the ribbon — when Work Offline mode is active, the button will appear highlighted or pressed in.

3. 3

   Click Work Offline once to toggle it off

   A single click turns the mode off. The status bar should change from "Working Offline" to "Connected" or show your account name, and Outlook will immediately attempt to deliver any messages waiting in the Outbox.

4. 4

   Trigger a manual send if the messages don't move

   Press F9 (or click Send / Receive All Folders in the ribbon) to force an immediate send cycle. Most stuck messages clear within a few seconds once offline mode is off.

Fix 2: Move the stuck message back to Drafts#

This is the fix for the second-most-common cause: a message that was opened from the Outbox while Outlook was mid-attempt to send it. When you open a message from the Outbox, Outlook puts the message into an editing state and stops trying to send it — the message stays in the Outbox folder, but the send process is paused indefinitely. Simply clicking it once to check the recipient can trigger this.

The important rule here is to never try to open a stuck message from the Outbox directly if you intend to re-send it. The correct sequence is to move it to Drafts first, then edit it if needed, then send again.

1. 1

   Do not open the message from the Outbox

   If you double-click the stuck message to read it, Outlook puts it in an editing lock and the situation gets worse. If you already opened it, close the message window first before attempting any of the steps below.

2. 2

   Drag the message from Outbox to Drafts

   In the folder pane on the left, click and drag the stuck message from the Outbox folder to the Drafts folder. Alternatively, right-click the message, choose Move, and select Drafts. This removes it from the send queue and breaks the editing lock.

3. 3

   Open the message from Drafts

   Now that it's in Drafts, opening it is safe — it's no longer in the send queue, so editing it doesn't cause a conflict. Verify the recipients and body.

4. 4

   Confirm the attachment (if any) is within size limits

   While the message is open, note the size of any attachment — if it's large, check Fix 3 before re-sending. Sending the same oversized file again will put you back in the same position.

5. 5

   Click Send and confirm it moves to Sent Items

   Send the message from Drafts. Watch the Outbox and Sent Items folders — the message should clear from Outbox and appear in Sent Items within a few seconds. If it gets stuck again, the cause is something deeper than the editing lock; move on to Fix 3 or Fix 4.

Fix 3: Check the attachment size limit#

Every email server enforces a maximum message size, and the limit that matters is the one on the receiving server, not just the sending side. Microsoft 365 allows outgoing messages up to 25 MB by default, measured as the encoded message size — which runs roughly 35% larger than the raw file size due to MIME encoding. A 20 MB file attachment, encoded, becomes about 27 MB, which is already over the 25 MB limit.

If the message goes to an external recipient, their server may enforce a different limit — Gmail's inbound limit is also 25 MB, but some corporate mail servers cap at 10 MB or less. Outlook usually shows a bounce or a non-delivery report (NDR) when the size is the problem, but it can also just leave the message sitting in the Outbox silently, which is why size is worth checking early.

1. 1

   Move the message to Drafts (as in Fix 2)

   Don't try to edit an attachment while the message is in the Outbox. Move it to Drafts first, then open it.

2. 2

   Check the raw file size of the attachment

   Open the message in Drafts and look at the attachment. Hover over it to see the size — if it's over 15 MB, there is a good chance the encoded version is pushing past the 25 MB server limit.

3. 3

   Replace the attachment with a OneDrive or SharePoint link

   In the compose window, click Insert, then Attach File, and choose Upload to OneDrive instead of attaching directly. Outlook will insert a sharing link rather than embedding the file — the recipient gets the same file, and the message size drops to kilobytes.

4. 4

   If the file must be attached directly, compress it first

   Right-click the file in Windows Explorer, choose Send to, then Compressed (zipped) folder, and check whether the compressed size is comfortably under 20 MB. If it's still large (video, raw photos, and some binary files don't compress meaningfully), the sharing-link route is the only reliable option.

5. 5

   Re-send from Drafts and verify it clears

   Send the updated message with the smaller attachment or the link. If it moves to Sent Items, the size was the cause. If it stalls again, continue to Fix 4.

Fix 4: Verify your account settings and re-authenticate#

When Work Offline is off, the message isn't locked in an editing state, and the size is within limits, the next candidate is an account or SMTP authentication problem. This is more common than people expect after a password change, a Microsoft 365 tenant security policy change, or a period where Outlook was left running without connecting. The send fails, but instead of telling you clearly what went wrong, Outlook just leaves the message in the Outbox.

Check the Send/Receive Progress dialog (Ctrl+Alt+S in classic Outlook) or the error log for a 535, 550, or authentication error before digging into settings — if an auth error is logged, you know what you're dealing with.

1. 1

   Check the Send/Receive error log

   In classic Outlook, press Ctrl+Alt+S or go to Send / Receive, then Show Progress, then Details. Look for any error line on the account that has a stuck message. An error code starting with 535 or 550 points to authentication; a timeout error points to a connectivity or server-side problem.

2. 2

   Open File, Account Settings, Account Settings

   Find the account associated with the stuck message, double-click it, and confirm the outgoing server (SMTP) address and port. For Microsoft 365: smtp.office365.com, port 587 or 465. For Gmail via IMAP: smtp.gmail.com, port 587. Confirm the "My outgoing server (SMTP) requires authentication" box is checked.

3. 3

   Click Test Account Settings

   Outlook will attempt to connect to both the incoming and outgoing servers and report any errors. A failure on the outgoing server test tells you the SMTP settings are wrong or the credential is rejected — fix the field it reports before proceeding.

4. 4

   Clear the saved credential and re-enter it

   If the settings look correct but the test still fails, go to Windows Credential Manager (Control Panel, User Accounts, Credential Manager, Windows Credentials) and remove the entry for this account. Reopen Outlook and sign in fresh when prompted. For Microsoft 365, this triggers a full modern authentication re-flow including MFA.

5. 5

   Run the Microsoft Support and Recovery Assistant (SaRA)

   Microsoft's free SaRA tool automates the diagnosis and reset of Outlook account and authentication issues. Search "Microsoft Support and Recovery Assistant" to download it. It covers edge cases — broken tokens, Conditional Access blocks, malformed profiles — that manual settings checks can miss.

Fix 5: Pause antivirus email scanning temporarily#

Most consumer and business antivirus products include an "email protection" or "email scanning" feature that intercepts outgoing mail before it leaves Outlook and scans it for malicious content. When the scanner holds the message for too long — or gets into a state where it can't complete the scan — the message stays in the Outbox indefinitely, with no error shown in Outlook itself.

This is most common on Windows machines running Avast, AVG, Norton, McAfee, Bitdefender, or Kaspersky with email integration enabled. The test is simple: temporarily disable the email scanning feature (not the entire antivirus, just the email component) and try sending again.

1. 1

   Open your antivirus control panel

   Look in the system tray for the antivirus icon, right-click it, and open the settings or protection panel.

2. 2

   Find the email or mail protection component

   Look for settings labeled "Email Protection," "Mail Shield," "Email Scan," or similar. The naming varies by product — consult the product's help documentation if you don't see it immediately.

3. 3

   Temporarily disable only the email scanning component

   Turn off the email scanning feature for 10 minutes or for the current session. Do not disable the entire antivirus — the goal is to isolate whether email scanning is the blocker, not to expose your machine.

4. 4

   Press F9 in Outlook to trigger a send

   With email scanning paused, press F9 to run Send / Receive All Folders. If the message clears immediately, the antivirus scanner was the hold-up.

5. 5

   Re-enable email scanning and consider switching to network-level scanning

   Once you've confirmed the cause, re-enable the antivirus feature. For a permanent fix, disable the email-integration (SMTP hook) component specifically and rely on the antivirus's real-time file scanning and web protection instead — those provide equivalent protection without intercepting Outlook's send process.

Fix 6: Repair the Outlook data file#

If multiple messages are stuck in the Outbox, pressing F9 does nothing, and other parts of Outlook behave oddly — search returning incomplete results, folders not loading, or a persistent "Disconnected" status despite a working internet connection — the Outlook data file itself may be corrupted. Outlook uses an .ost file (cached Exchange or IMAP account data) or a .pst file (local or imported data) on disk, and either can develop corruption over time or after a crash.

Microsoft ships a repair tool for this: Inbox Repair Tool, also called ScanPST.exe. It scans the data file for errors and rebuilds the index — it's non-destructive, it keeps your mail intact, and it's the right step before you reach for a full profile rebuild.

1. 1

   Close Outlook completely

   Outlook must be closed before you run the repair tool — if OUTLOOK.EXE is running in Task Manager, end it before proceeding.

2. 2

   Locate ScanPST.exe

   The location depends on your Office installation: on most Office 365 / Microsoft 365 installations on a 64-bit Windows machine, it's at C:\Program Files\Microsoft Office\root\Office16\SCANPST.EXE. On 32-bit installations or older Office versions, check C:\Program Files (x86)\Microsoft Office\root\Office16\SCANPST.EXE. You can also search for "scanpst" in File Explorer.

3. 3

   Locate your Outlook data file

   Before you can run the repair, you need the path to your .ost or .pst file. In Outlook (before closing it), go to File, Account Settings, Account Settings, then the Data Files tab — the path is listed next to each account. Write it down, then close Outlook.

4. 4

   Run ScanPST and point it at your data file

   Open SCANPST.EXE, click Browse, navigate to the .ost or .pst file from the step above, and click Start. The tool will scan the file and report any errors — this can take several minutes on a large mailbox.

5. 5

   Repair and check the backup option

   If ScanPST reports errors, click Repair. Leave the "Make a backup of scanned file before repairing" option checked — it creates a copy of the pre-repair file in case anything goes unexpectedly. The repair pass usually completes in under five minutes.

6. 6

   Reopen Outlook and attempt to send

   After the repair, open Outlook and press F9. On a large mailbox, Outlook may take a few minutes to rebuild its index before it's fully functional — give it time before concluding the repair didn't work.

Fix 7: Rebuild the Outlook profile (last resort)#

If every previous fix fails to unstick the Outbox, or the fixes hold for a session but the problem comes back, the Outlook profile itself may be corrupted. An Outlook profile is the configuration layer that ties your account credentials, settings, and local data file together — it's separate from your actual mail, which lives on the server. Rebuilding it is the most disruptive fix in this guide, but it's also genuinely the last thing to try, and it works when nothing else does.

Your messages are not at risk. Exchange, Microsoft 365, and IMAP accounts store the actual mail on the server. Creating a new profile re-syncs your mail from the server rather than deleting it.

1. 1

   Close Outlook

   Fully close Outlook and confirm OUTLOOK.EXE is no longer in Task Manager.

2. 2

   Open the Mail control panel

   Search for "Control Panel" in the Windows Start menu, then open Mail (or Mail — Microsoft Outlook 2016, depending on your version). Alternatively, search directly for "Mail (Microsoft Outlook)" in Windows Settings.

3. 3

   Click Show Profiles

   This lists your existing Outlook profiles — most people have exactly one, named "Outlook."

4. 4

   Add a new profile

   Click Add, name the new profile something like "Outlook2" or "Fresh," and walk through adding your email account exactly as you would on a new machine.

5. 5

   Set the new profile as the default

   In the "When starting Microsoft Outlook, use this profile" dropdown, select the new profile name. Click OK.

6. 6

   Open Outlook and confirm the account syncs

   Outlook will connect to the mail server and begin re-syncing your mailbox. On a large mailbox, this can take time — wait for the initial sync to settle before testing the Outbox.

7. 7

   Send a test message and confirm it clears

   Compose a short test email to yourself. If it sends and appears in Sent Items, the profile was the problem. Leave the old profile intact for a few days as a fallback before deleting it.

8. 8

   Delete the old profile after confirming stability

   Once the new profile has run cleanly for several days, go back to Control Panel, Mail, Show Profiles, select the old profile, and click Remove.

Diagnosing fast: which cause do you have?#

Before reading down the whole fix list, use these shortcuts to narrow the cause to a single candidate.

• Status bar says "Working Offline" — this is Fix 1, and it's almost certainly the cause. Toggle Work Offline off and press F9.
• You clicked on the stuck message to read it — this is Fix 2. Drag it to Drafts, then re-send from there.
• The message has a large attachment (over 15 MB) — this is Fix 3. Move it to Drafts, replace the attachment with a OneDrive link, re-send.
• Other messages are also failing to send, or Outlook is showing a credential prompt — this is Fix 4. Check account settings and re-authenticate.
• The message sits in the Outbox for a long time and then sometimes clears on its own — this points to Fix 5 (antivirus scanning) or a slow outgoing connection.
• Multiple messages are stuck and pressing F9 produces nothing, with other Outlook functions also misbehaving — this is Fix 6. Run ScanPST on the data file.
• You've done every fix above correctly, in a fresh session, and the Outbox stalls again the next day — this is Fix 7. The profile itself is corrupted.

How to prevent emails from getting stuck in the Outbox#

Preventing the problem is mostly about two things: not triggering the editing lock accidentally, and keeping the conditions that break the send cycle from building up in the first place.

• Never click a message in the Outbox while it's in the process of being sent. If you need to check on a message that's been sitting there too long, wait for the current send cycle to complete (usually a few seconds), or move it to Drafts using a right-click rather than opening it.
• Share large files as links, not attachments. OneDrive, SharePoint, Google Drive, or Dropbox links side-step the server size limit entirely and keep both your Sent Items and the recipient's inbox lean.
• Keep Outlook and Office updated. Several outbox-stall bugs in the past two years have been fixed in incremental Outlook updates — a client running months behind on updates is carrying known bugs you don't need.
• Don't leave Work Offline enabled as a "quiet hours" setting. It's a legitimate mode for working without network access, but it's easy to forget to toggle it off, and a stuck Outbox full of overnight replies is a predictable result. Use scheduling (delay delivery) or a Do Not Disturb approach at the OS level instead.
• Keep your antivirus and Outlook compatible. If your antivirus software has a compatibility update for a recent Outlook release, apply it. Email scanning hooks that worked fine on an older build can stall the send queue silently on the new one.
• Run ScanPST periodically on a large, heavily used Outlook profile — not just after things break. It's a maintenance tool as much as a recovery one.
• If the Outbox stalls after a password change, restart Outlook immediately and re-enter credentials rather than letting it sit in a failed-authentication loop. The longer it retries with bad credentials, the more likely the account ends up in a lockout state.

Classic Outlook vs. new Outlook on Windows vs. Outlook on Mac#

The fixes above are written for classic desktop Outlook on Windows — the version with the full ribbon. The new Outlook on Windows and Outlook on Mac behave somewhat differently at the edges.

The new Outlook on Windows does not have a Work Offline mode button, so Fix 1 doesn't apply. It also manages its data file differently — there is no local .ost to repair with ScanPST in the new Outlook, which makes Fix 6 irrelevant. If the new Outlook has a stuck message, the most common fix sequence is Fix 2 (move to Drafts) and Fix 4 (verify account settings and re-authenticate), since the new client manages connectivity automatically and surfaces auth problems more directly than the classic client does.

Outlook on Mac uses Keychain Access for credential storage rather than Windows Credential Manager, and its data file format is different — there is no ScanPST equivalent. The Mac equivalent of a profile rebuild is removing the account and re-adding it from Outlook preferences. The Work Offline setting does exist in Outlook for Mac and is the same first thing to check.

Outlook on iOS and Android typically stall because of an expired OAuth token or a connectivity issue. Remove and re-add the account from the mobile app's settings — that forces a fresh token exchange, which clears most mobile outbox stalls.

The common thread through most of these causes is that Outlook's send process breaks silently — Work Offline is on and the status bar says so if you know to look, but the application itself doesn't interrupt you or explain why a message is sitting in the Outbox for an hour. We build AI Emaily, which connects to Outlook alongside Gmail, iCloud, Fastmail, Proton, and any IMAP inbox through a unified connection layer, and it surfaces a clear send and delivery status rather than leaving a message in a gray area between "sent" and "failed." If you've spent time digging through Credential Manager or Outbox folders for the third time this month, moving that inbox into a client that makes the connection state explicit is a smaller fix than any of the seven above.