mail routing

[Rodian Paul]

I have a 4D/70 (gungadin) and a CS12 (sabu) both running NFS. 
I want to keep all mail on 'sabu', so in my /usr/lib/aliases on
'gungadin' all mail gets forwarded to 'sabu'. 

The problem is that I want to notify users who are logged onto 
'gungadin' that they have mail on 'sabu'. 

If I execute a shell via cron on 'sabu' to send a message via mail 
to the user on 'gungadin' that they have new mail on 'sabu', the mail
obviously gets re-routed back to 'sabu'.

Given that I'm a novice at this stuff, can anyone offer a solution to
this problem?

Cheers,

Rod.