I'm using MySQL Database for my Private Message service..
but my forum has a lot of users.. so is that better to move in FTP place of MySQL?
if so.. then what will happen to the current Users PM in database?
can I move them also or those will be deleted?
Thanks

You mean flat files, not FTP I think. I think it may be possible using a custom script, but only Paul would answer that ;).

PM module really has two options - flat files or mySQL, but if you move from one to the other, the data kept in one module won't be transferred automatically.

To transfer it, you really would need to program a special script, but in general, you may just inform your users that you will swap the data and they should save it some way (or Export like it's provided in the recent version of this add-on).

I don't think PM are the most important part of forums, you need more public content for ads and search engines :-)