First things first!
i want to block Webmail attachment i dont have any mail server
doesn't really describe the problem you're trying to solve.
So first write what mail do you want to block ?
- is it your server a 'relay' for sending emails to the internet
- are you receiving emails with attachments that you want to block
- what user accounts (email acc.) possibly you have on your server you want to block emails (or is it just you as 'root')
- what is the MTA on your server (postfix, sendmail ...)
Whether you ask your question the right way it's possible you will get the answer.