Perhaps the .pst or .ost file is greater than 20 GB. I think that was the maximum in Outlook 2010.



Check the size of the file. If it's over 20 GB...



1. You may be able to open Outlook without crashing if you start it in Safe Mode. (Hold down Ctrl while opening the application.)


If you get in...


2. Delete as many email messages as you dare. For example, messages in your inbox that are bigger than (say) 1 MB; draft messages that you're never going to send; etc.


3. Delete everything in the Deleted folder.


4. Compact the mailbox. This is the only way to shrink the .pst or .ost file. Deleting messages does not actually reduce the size of these files!



5. Exit Outlook, and restart it normally.