Could the index of dovecot be stored in database?

Hi dovecot, I have a question about the index of dovecot. I had read the wiki, and saw that I can custom a Input streams to do read/seek/sync...by implementing a istream-*.c file. Thus maybe dovecot can read mail from a http server or any others. But I found that the index of maildir can't extend very well. There is no extern API for developer? For example, I want to put the index to database(maybe, MySQL) or any else, But I found I have no way to implement it, Unless a heavy modification?

-- eSX