Dovecot Submission - rate limiting

[itanguy at univ-brest.fr]

Hello,

is there any way to rate limit submission mail (counting per user) when 
using Dovecot/Submission (no Postfix)?

Using a milter seems impossible.
Using Dovecot Events seems "too" global (not per users discrimination).
Maybe rate-limiting has to be external and then include in the pass_db 
query ?


Thank your for any hints.
Ismaël Tanguy