If outlook keeps opening in Safe Mode, this could be due to a KB Microsoft pushed out (KB3114409). This was removed by Microsoft as it did’t work as expected.
To resolve the issue remove the KB from the client machine. If there is a WSUS server on site it will also need the update Approving and the Approving for Removal. Set a deadline to make it happen ASAP.
https://support.microsoft.com/en-us/kb/3114409