This time of email-to-DB action has been done in the ecommerce/customer-service piece. It is easiest to immediately insert the message into the DB using Perl/DBI on the email receiving end. At ArsDigita, it has been done using Perl/DBI, Java Mail, and Netscape Mail plugins.
The POP idea is not bad, but could get complicated to do POP support. If you could do it well, though, it would be more scalable than a Perl/DBI process and db connection on every incoming email.
One last note: think very hard before you enable incoming email to your bboards. Yes, it's convenient, and because it's convenient, it will lower the bar for content submission, and usually increase the noise on your bboards. We have no plans on enabling this on OpenACS.org.
