Solve Stuck Outlook Outbound Message Problems

Exit and restart Outlook (this often works).

Make sure you have network connectivity and that your mail server is available (can you connect to it via web access for example, and does it work from your phone?).

Place Outlook in Offline mode, then Online (Select the Send/Receive ribbon and select Work Offline, then after 20 seconds deselect Work Offline).

Check that your antivirus supports Outlook and isn't interfering with the moving of messages from the Outbox to Sent (e.g., did you just change your anti-malware solution?).

Look at which snap-ins you have enabled and try disabling (File, Options, Add-Ins, Manage COM Add-ins, Go, which allows add-ins to be disabled or removed). For example, I found the Outlook Social Connector 2013 was causing problems for my installation. If disabling a snap-in caused Outlook to hang, that's probably the guilty snap-in, so try the next step.

Start Outlook in safe modeoutlook.exe /safeThen try disabling snap-ins, and restart Outlook.