Outlook Cannot Send Or Receive Since PST File Too Big

If you find that your PST file is too big and Outlook won’t let you delete emails or empty the trash can, you might be able to slowly free up space by deleting emails individually.

The trick is to hold down the SHIFT key and then press delete. This will permanently delete the email rather than send the email to the trash can which is not work since the trash can is already too full.