Verisign Cert

[Linux Addict]

Hello Gurus, Currently my postfix server runs with self-signed cert, but now
I was asked to implement verisign cert for some of the outgoing mails.  My
question is when the verisign is cert installed, will all the outgoing mails
such as toyahoo.com, gmail.com will be encrypted? Do the clients neeeds any
certificate information?  I am not very clear. Please throw some light..
~LA