[BlueOnyx:10340] Sending one site's email via a separate IP

[Dogsbody]

Has anyone done this?  I have one site that send a lot of mail and I 
don't want their mail affecting the reputation of the rest of the sites 
on this server.

Moving their website to a separate IP is easy however their email will 
still be sent via the main IP of the server.  Before I dive headlong 
into conf files,  does anyone know how to setup sendmail so that email 
for one domain is sent via a virtual IP instead of the main one?

Any pointers welcome.

Thank you

Dan

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