1. Try to Re-send the message:
i.) Click on Send All on the Send/Receive tab in Outlook.
ii.) Check your Outbox to see if the message is gone.
2. The message size too large.
A message can get stuck if it includes an attachment that’s too large for some email servers to handle. For example, your workplace might limit the size of email messages you can send or receive. That slide deck with lots of pretty pie charts might be the culprit.
If re-sending the message didn’t work, try reducing the size of the attachments and send it again.
i.) To do that, you might first try to either delete or open the message in the Outbox. But that might not work. You can’t open or delete a message if it’s doing that. Instead, you’ll probably see this message:
ii.) To stop Outlook’s wheels from turning, you can go offline. On the Send/Receive tab, click Work Offline.
iii.) Now you can open the message, remove the attachment, reduce its size, and re-send it. Or you can delete the message and start from scratch-if of course you have a copy of the attachment.
3.) Email server is offline:
Sometimes Outlook can’t send your messages because your email server is offline–whether an email server at work or online.
i.) Please check your server is offline. If yes you may see “Disconnected” in the Status bar.
Note : Please submit us ticket if you need further assistance after done above troubleshooting.