Firewall doubt about blocking webmail sites

[Marinho Paiva Duarte <marinho_linux@yahoo.com>]

Hi!!

I would like to know how can a block webmail sites like yahoo?
I trying to do it because 70% of my network traffic is of people getting their e-mails in these sites.
Many people said to block by ip address, but there is several machines awnsering connections in these
sites. I don't know all the ip address... And and don't want to know, of course.
P.S.: I use masquerade.

Thanx...

Marinho Paiva Duarte

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