A problem plaguing some users affects Outlook meeting requests: they won’t leave the Outbox. Email sends just fine, but meeting requests are stuck in the Outbox. They will send if the users opens Outlook in safe mode, which points to problems with an add-in, specifically Norton Antispam Outlook Plugin.
To disable the add-in in Outlook 2010 or Outlook 2013:
- Go to File, Options, Add-ins
- Click the Go button at the bottom of the window
- Find the Norton Antispam Outlook Plugin and deselect it.
- Click OK and return to Outlook.
The meeting requests should send. If not, open each meeting request and click Send.
You may be able to re-enable the Norton add-in if you repair the Office installation, some users reported that all future meeting requests send. While you can certainly try it, using a virus and spam scanner on the server and removing the spam at the mailbox level, before Outlook downloads it, is a better solution and should be used whenever possible.