Allusers Email with Sendmail

["Daniel Hooper" <dhooper@ofc.emerge.net.au>]

Please excuse my complete lack of skill and knowledge with shell
scripting /
awk / sed & sendmail, I'm trying to put something together to email all
User's for an ISP. I've researched a little bit and found this command
(modified to suit my environment)

red:/var/yp/# awk -F: '$3 > 100 { print $1 }' `ypcat passwd` >
/etc/mail/allusers

and I get this: 

bash: /usr/bin/awk: Argument list too long

So my question, how do the rest of you ISP/Sendmail guru's do it ?

A kick in the right direction would be very much appreciated.

Regards,
Daniel Hooper