[exim] How to not process emails with attachments over 15MB

Hello all,
basically what I want is that EXIM could delete or deny any email that has
an attachment higher than 15MB.

It will be really nice if EXIM could deny any email that contains N user x
attachment that could be higher than 15MB, I mean if a user sent an
attachment of 5MB to 100 users, that is 500MB and its higher than 15MB
allowed.

Sorry if this has been asked before, if so, please lead me to the thread so
I can look at it, thanks.

Best Regards,

Sergio Cabrera