We have a mail server running Zimbra (ZCS 6.0.8). The server has 5 active public IP addresses in the same subnet. (.226-.230). I currently have A records for each of these (host0.domain.com..host4.domain.com), with the main host.domain.com of the machine pointing to .226.

Our host has ended up being listed on the SORBS DUHL list (even though it's in a server farm). According to them you can get removed quickly by checking that your host has an MX record, an A record, and a PTR record that points back to the hostname given in the MX record.

I tried setting the PTR records so that each of these addresses resolved back to their A record (i.e. .228 had a PTR to host2.domain.com). However, I then got mail being rejected from other servers because when Postfix (under Zimbra control) sends out mail, it uses the main hostname for the HELO - there doesn't seem to be any way to override it. So the PTR records currently say host.domain.com for all 5 IP addresses.

What's the correct way to handle this? Should I have an A record for the domain that points to all the IP addresses (for round-robin handling)? I'm nervous of changes that could cause problems, so I'm wondering what the standard way to handle a multiple-IP-address mail server is.