1:1 2 different publ. IP to 1 local IP?

[fips]

Hi,

I want to know if its doable to use 2 different public IPs to the same local IP on 1:1 NAT?
It was possible to enter in the pfsense gui the second public IP and set up to the local IP.
But I deleted it afterwards not to risk something.

Background:
I want a second public IP for the mailserver, in case the first IP is listed on blacklists.
So my plan was to have the first correct 1:1 NAT listed on the top and the backup IP on the bottom of the 1:1 list.
If the original IP gets blacklisted I would switch the pub. IP at DNS and it would smoothly start to work with the new IP.

I hope I explained everything more or less clear.