I am having a dedicated server and hosted multiple domains and my clients wants to have some restrictions sending emails , I am looking for a solutions for following

1. Need to Restrict Sending emails with Attachments
2. Need to Restrict Sending Emails to Public Domains (like yahoo, gmail, live.com, hotmail)

1. Need to Restrict Sending emails with Attachments
my vps server has multiple domains , each domain users has many email users , they want restrict their user to send emails with attachments to their receipients.*

Eg: some user not allowed to send emails with attachments , if any user's send emails with attachemnts automatically deleted by the server and only mails contents should reach to their recipient.*
some of the user are allowed to send emails with attachments,*
also if any one send emails with attachment that particular domain administrator should get the email notifications with who sents emails with attachments , subject of the email id, Attached file name .

2. Need to Restrict Sending Emails to Public Domains (like yahoo, gmail, live.com, hotmail)

another request my clients wants to restrict their mail user (some mail users) to send mails to public domains like yahoo, gmail, live.com, hotmail mail id's , some users are allowed to send emails to public domains as mentioned above.