After a little more digging, it appears the Pronto is a fork of CSCMail. The Pronto site says it was forked when CSCMail went to C. The CSCMail faq says version 2 will be in C w/o SQL. But the current version 1.6.2 is still in perl/gtk. His reasoning for no DB makes sense to me. So you decide. :-)
Why do you need the message store to be a SQL database?