Postfix: Limiting the number of messages per smtp connection

[Anders Nielsen <anielsen diku dk>]

I am trying to deliver around 50000 personalized emails to our users
every night.

A major ISP in this country has put a limit on their mail servers so
they only accept 20 messages per SMTP connection. This is done to
prevent spam.

Is it possible for me to limit postfix so it only sends 20 mails per
SMTP connection?

Thanks in advance 
  Anders Nielsen