Preventing HotMail,AOL,Pop3

What is your mail client?

You need to institute a group policy for the mail clients that prohibits users from adding accounts.

You also need to block users from installing other mail clients that would bypass your block.

Chas

It depends on what programs you are using to access the internet ( you didn't specify that)
Since you are running nt I will give an nt based solution with a MS program.
You can use MS Proxy server 2.0 or newer ISA server to specify with programs can access the internet (if you install the proxy client, and define the protocols).
Therefor p2p programs, chat programs etc won't access the internet unless you specify them on the proxy/isaserver.
For webbased email blocking like Yahoo and hotmail, you will have to use Surfcontrol which will enable you to block websites on a lot of options (content, categorie , etc).
If's only a couple of websites you want to give access to you can use proxyserver/isaserver, if the company policy is to giveaccess to all wbsites except explicit ones , it's better to use surfcontrol.

Regards
Leopold

install proxy server 2.0 or isaserver.
You will be able to block all programs that you did n't specify (you will have to install the proxyclient to, in order to do so).

Install surfcontrol so you can block access to all websites that you dont' allow, including hotmail and yahoo.

Note that other programs like winroute , etc nowadays also have similar options but maybe not as detailed as the ones I mentioned above.

Leopold