How to Restrict Emails?

Is there any way in suse to restrict users from sending email from yahoo/gmail (or) i need to block users from sending attachments. Or I need to get a copy of the mail to admin mail.

Kindly help me.

yahoo-mail/gmail etc. are browser based (of course, gmail accessed from a mail client too) and you need a proxy setup to control users.
squid is a good proxy.

Thanks. Can i have a copy of emails to admin mail account if i use squid?

As I mentioned in my post, the users are technically not sending emails when they use yahoo-mail, gmail etc. They are typically “uploading/downloading” content and their email messages are part of the content.
There are many options in squid to control traffic and log what they are doing including what they upload/download etc.