Maybe you can set a maximum amount of pm's per inbox, so it won't hog up a lot of memory overtime. But then you would also have to set it up so a person would be informed when they try to send a message to someone with a full inbox. But if you do that, you need to make it so that a moderator (such as yourself) can overwrite that and send a message to a full inbox. (That way some one can't fill their inbox to avoid getting messages from an mod telling them to 'please stop adding fake compounds' etc.)
Maybe you can set a maximum amount of pm's per inbox, so it won't hog up a lot of memory overtime. But then you would also have to set it up so a person would be informed when they try to send a message to someone with a full inbox. But if you do that, you need to make it so that a moderator (such as yourself) can overwrite that and send a message to a full inbox. (That way some one can't fill their inbox to avoid getting messages from an mod telling them to 'please stop adding fake compounds' etc.)
Oh, and thanks xD