MS Outlook XP and earlier
These all have something insane in common, they can only open pst files that are 2GB or less, but they’ll write those files until well over that limit. So the next time Outlook opens it just sort of spazzes out.
Fun yes?
There’s a tool to truncate the file, from MicroSoft, but it doesn’t seem to follow any sane pattern or allow you any kind of selectivity.
Definitely fun. The only options from here are to change mail clients (I suggest Thunderbird) or upgrade to a later version of Outlook. I don’t suggest that because then you’ll still be using Outlook.