[Dovecot] Using MySQL to store email?

[Marc Perkel]

Timo,

the idea of a MySQL backend isn't because you want to win a speed 
contest against other storage methods. The idea is because with MySQL 
you can do things that would be nearly impossible without a database. 
There are things I'd like to do that are basically unthinkable now. 
Databases would allow me to do indexing on a whole new level. I could 
add awesome featues to my email system and it would be incredible for 
spam control.

On example for spam control. Suppose a spam attack comes in delivering 
the same spam to thousands of users. And suppose that my system didn't 
realise it was a spam until after the spam was delivered. I could delete 
all email from that host for all users in seconds if I make the sender's 
host address a key field. You can't block spam retroactively without a 
database.