Hello Jamie Blackburn, thanks for posting this in the community.
When emails stay in the Outbox and only send or receive from time to time, it usually means Outlook is having trouble staying connected to the mail server. Check if Outlook shows Working Offline or Disconnected, because it will not send or receive until it reconnects. Make sure your internet connection is stable, since a weak or changing connection can cause emails to remain in the Outbox without showing that they were sent. If you use antivirus software or a VPN, try turning them off for a moment, as they can interrupt Outlook’s sync. You can also restart Outlook and use the Repair option in Account Settings to fix the connection. If the issue continues, creating a new Outlook profile can help, especially if the current profile is corrupted.
Kind regards,
John Oli