[Dovecot] Deliver limit based of number of destination recipients and size of mails, any option to do that?

I have a mail server with postfix, dovecot (1.2.15) and deliver lda (dovecot) with 350 users. I have the problem that in this christmas the employees are sending some big files (mainly powerpoints files) to a lot of recipients, because of that the server get a lot of charge (is a Xeon quad core 5405 with 4GB of Ram), i have four disks in Raid 5 configuration (HP E200 controller, not very fast) Is there any option to limit this type of delivery, the total size of the mails delivered to each user (total recipients * size of mail), in dovecot deliver. I don't want to limit the concurrent delivery more lower than 350 recipients and the max size of the mail we can send is 15M. Thanks a lot,

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Andrés Fernando Yacopino