Message Stuck in the Outlook Outbox and Won't Send? Here's the Fix
You hit Send, but the message just sits in the Outbox and never goes out.
Why: The most common causes are a too-large attachment that can’t upload, Outlook being in Work Offline mode, or the message having no scheduled send pass. Stop it from retrying first, then fix the cause.
Fix 1: Go offline so it stops re-trying
A stuck message keeps attempting to send, which can lock the Outbox. Park it first.
- Send / Receive tab → click Work Offline (the button highlights when offline).
- Now you can safely open or delete the stuck message without Outlook grabbing it mid-send.
Fix 2: Check for an oversized attachment
This is the single most likely cause. Most mailboxes reject attachments over about 20–25 MB.
- Open the Outbox and double-click the stuck message.
- If it has a large file attached, remove the attachment (click it, press Delete).
- Re-send with a smaller file, or upload the file to OneDrive and send a share link instead.
- Click Send.
Fix 3: Re-open and re-send the message
A message can stall simply because it never got a send pass.
- With Outlook offline (Fix 1), open the Outbox and double-click the message.
- Click Send again to re-queue it.
- Turn Work Offline back off, then Send / Receive → Send/Receive All Folders (or F9).
Fix 4: Turn on “Send immediately when connected”
If messages only leave when you press F9, this setting is off.
- File → Options → Advanced.
- Under Send and receive, tick Send immediately when connected, then OK.
(If the box is greyed out, a group policy controls it — ask your IT admin.)
FAQ
I deleted the attachment but it still won’t move — why? The half-sent message can be locked. Use Fix 1 to go offline first, or if Outlook won’t respond, close it via Task Manager (end outlook.exe), reopen, and the Outbox unlocks.
Could a full mailbox cause this? Yes — if your mailbox is over quota you can’t send or receive. Empty Deleted Items and Junk Email, or archive old mail, then retry Send/Receive.