If Outlook is being used by another program e.g. Getting scanned by an antivirus tool, then it could cause the emails in the Outbox to get stuck. Top 4 Solutions to 'Email Stuck in Outbox' Issue in Outlook 2016/2013/2010 1 Change Outlook Connection Status. Your emails can get stuck in Outbox.

Here are some thoughts.

1) As for emails getting stuck in the Outbox, I frequently find that they users have exceeded their quota. If they are using Cached mode, it's not real obvious. Have them clean out their emails more frequently. Also, if you are able, consider not using outlook in cached mode.

2) Just to make it more obvious, you could right-click the Outbox and add it to the users' favorites.

Where Did My Outbox Go In Microsoft Outlook For Mac Windows 10

3) You do know the trick about moving the stuff stuck in the Outbox, right? Drag the message to Drafts, then open the message, click send.

Not sure if that helps out much but those tips helped us some.

Where Did My Outbox Go In Microsoft Outlook For Mac 2017

Todd