Centralised mail journalling

I’m about to implement mail journalling, and am perfectly happy with the work I need to do on my first server, since that will be copying mails to a local journal database. However, my first question is whether anyone knows of any issues if I set up a mailin database record in my NAB pointing to that local journal database (since the name of the live journal db will always be the same), then allow the local server to manage the database by rolling over when the db hits a set size. Presumably, if the process of rolling over starts with a pause of the router task, this should all work fine. Any ideas?

My second question is what header information is contained in the mail that hits the mailin database. Is it the original header info of the mail being journalled or does the process of sending it to a mailin database make it a new mail in its own right?

Comments/thoughts gratefully received, although no blazing hurry since this is just a bit of preliminary planning.