You hit Send in Outlook and the email disappears from your compose window — but instead of showing up in Sent Items, it's sitting in your Outbox with no sign of going anywhere. You try sending again, nothing happens. You close Outlook and reopen it, and it's still there.
A stuck Outbox is one of the most common Outlook problems across both the desktop app and the web version, and it almost always has a specific, fixable cause. Here's how to diagnose it and clear it — without losing the email you're trying to send.
Why Outlook Emails Get Stuck in the Outbox
A large attachment is slowing or blocking the send queue Outlook processes outgoing emails one at a time, in order. If one email — even one you sent earlier — has a large attachment and hasn't finished uploading, every email behind it in the queue is blocked. This is the most common cause of a stuck Outbox, and it's often an email you sent hours ago that you've already forgotten about.
Outlook is working offline Outlook has a manual "Work Offline" mode that disconnects it from the mail server without closing the app. When this mode is active, emails queue up in the Outbox and won't send until you switch back online. The mode is easy to accidentally toggle and doesn't always display a prominent warning.
An authentication token has expired Outlook maintains a connection to your mail server using a cached authentication token. After a password change, a Microsoft account update, or an extended period of inactivity, this token can expire. Outlook may appear to be connected but fail silently when trying to send because it can't authenticate with the server.
A corrupted email in the Outbox If Outlook crashed or lost its connection partway through preparing an email for sending, the resulting draft in the Outbox can become corrupted — meaning it can't be sent or deleted through normal means. This corrupted email blocks the entire queue.
Step-by-Step Fix
Step 1 — Check if Outlook is in Work Offline mode
In Outlook desktop, click the "Send / Receive" tab in the ribbon at the top. Look for a button called "Work Offline." If it appears highlighted or pressed in, Outlook is in offline mode. Click it once to switch back online. Wait 30 seconds and check whether the stuck email sends.
This single step resolves the problem in a large number of cases. It's worth checking before anything else.
Step 2 — Open the Outbox and check for large attachments
Click on your Outbox folder in the left panel. Look at every email in there — not just the most recent one. If you see any email with a large attachment (anything over 5MB is worth investigating), that email may be blocking the queue.
Right-click the email with the large attachment and select "Delete" or move it to Drafts. Once the blocking email is removed, the rest of the queue should process. If you still want to send the large file, compress it first or use a file sharing service like OneDrive and send a link instead.
Step 3 — Switch Outlook to offline mode, delete the stuck email, then switch back online
If the stuck email won't open or won't delete while Outlook is trying to send it, force Outlook into offline mode first (Send / Receive tab > Work Offline), then try to open and delete the stuck email from the Outbox. Once it's deleted, switch back online. This technique works because it stops Outlook from actively trying to process the email while you're attempting to remove it — trying to delete an email that Outlook is actively sending can cause it to get locked.
Step 4 — Re-enter your account password
Go to File > Account Settings > Account Settings > select your email account > Change. Even if your password hasn't changed, re-entering it forces Outlook to refresh its authentication token. Click Next, then Finish, then close and reopen Outlook. Try sending a test email.
Step 5 — Repair your Outlook profile
If none of the above works, your Outlook profile may have become corrupted. Go to Control Panel > Mail > Show Profiles > select your profile > Properties > Email Accounts > select your account > Repair. Follow the prompts. This process re-establishes the connection between Outlook and your mail server without deleting your emails or settings.
If You're Using Outlook on the Web (outlook.com or Microsoft 365)
The steps above apply to Outlook desktop. If you're using Outlook on the web and emails are stuck, the fix is simpler:
Check your browser extensions first — the same way ad blockers can interfere with other platforms, they can block Outlook's web interface from completing send requests. Try sending from an incognito window with no extensions running.
Clear your browser cache if the incognito test works — go to your browser settings, clear cached files for the last 7 days, and try again in your normal browser window.
Check your mailbox storage quota — if your Microsoft account or Microsoft 365 mailbox is full, outgoing emails are blocked. Go to outlook.com > Settings > General > Storage to check your current usage.
Pro Tip: Create a Test Email to Diagnose the Queue
Before deleting anything or changing settings, send yourself a short test email with no attachments — just a one-line message to your own address. Watch the Outbox carefully for 60 seconds.
If the test email sends immediately and your original stuck email stays behind, the problem is specific to that email — the file attached to it is too large, the format is unsupported, or the email itself is corrupted. Delete it, recreate it, and try again.
If the test email also gets stuck in the Outbox, the problem is with Outlook's connection to the mail server — authentication, offline mode, or a server-side issue. Work through Steps 1 and 4 above.
This test takes 60 seconds and immediately tells you whether you're dealing with a problem-email issue or a connection issue — which means you're not wasting time trying fixes that don't apply to your situation.
One More Scenario: Emails Sending but Not Arriving
If your emails leave the Outbox and show up in Sent Items but the recipient says they never arrived, the issue is different — either the recipient's spam filter is catching your messages, your sending domain has a reputation issue, or the recipient's email provider is rejecting messages from your address.
Ask the recipient to check their spam or junk folder first. If the email is there, ask them to mark it as "Not spam" to train their filter. If it's not in spam either, contact Microsoft Support at support.microsoft.com — this type of delivery failure requires server-level investigation that goes beyond device troubleshooting.
Last updated: June 2026. Steps are based on Outlook for Microsoft 365 (desktop) and Outlook on the web. Steps may vary slightly on Outlook 2019 or earlier versions.
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