Postfix for three domains on one host

[Andrew Bernard]

I want to use my single VPS for three distinct domains. Simple for 
webservers. I would also want to be able to send and receive email on 
the three domains using Postfix. I understand there is postfix-multi. 
Everything I have read so far uses separate IP addresses for this 
scenario. Most VPS providers are loath to assign more than one or at 
most two IPV4 address to a VPS, due to the global shortage. I have been 
unable to get three at Linode.

Not just subdomains, but quite distinct ones. For example (just abstract 
names)

ab.space

cd.space

zx.com


The obvious solution is to run three VPS's. But this adds expense and 
triples the admin overhead. is there any way to configure Postfix to act 
for three separate domains without the necessity of separate IP's?

Pardon me if this is a stupid newbie question, but it seems to me that 
Postfix is enormously powerful and can do pretty much anthing if you 
know how.

Andrew