Most of my mail is delivered by smtp directly to me, but my
secondary max records cause some mail to be delivered to a POP3
mailbox- this is then retrieved using spamassasin.

This works very well generally - I get my mail very quickly and implement spam/virus filtering.
The only problem is that many spammers deliberately target secondary
mail servers as being less likely to have spam filtering, so I still
filter mail received vi fetchmail even though this is seen by my mail
server as local mail.

In order to allow my mail client to deliver to the server without
waiting for the spam scan I have configured the server to listen on two
local ip addresses (127.0.0.1 and 127.0.0.17) fetchmail delivers to the
first which is filtered - my mail client delivers to the second - and
mail to this address is accepted without spam scanning