I've had to delete a few posts by "AllMonks", and a couple other members I banned -- but generally speaking posts here are permanent. You can browse posts on CathInfo all the way back to 2006!
PMs, however, are another story. They get purged regularly. CathInfo does not have its own server, so it must deal with "shared webhosting" and the limitations thereof. In other words, CathInfo can't afford to be your Gmail.
If you want to archive important discussions or docuмents you received via PM, you can print out hard copies, print them to PDF, cut & paste them into text files, etc.
CathInfo can't store months and years worth of private messages like a Gmail account. CathInfo's resources have to be saved for more important stuff -- like posts. We're getting close to 300,000 of those.
If you've lost anything important in the PM purges, I'm sorry. They get deleted in a bulk manner based on their age. With something like private messages, that's the only way to go.