I set up and ran a couple of mail servers on ipv4 address on amazon ec2. These addresses were previously blacklisted and it took some work to stop some emails from getting blocked. The other problem is that amazon limits you to only 5 elastic ipv4 addresses per region (an elastic ip is equivalent of a static ip).
I plan to set up other mail servers on ec2. To avoid the problems above, I want to set up the mail servers with ipv6 out of the box and I want that ipv6 address to be the main static ip address for the machine and basically ignore the ipv4 address (except for when using ssh, etc.).
Is this possible? Will I run into problems with some mail servers not being able to talk to my ipv6 machine because they are ipv4? If so, is it possible to advertise the non-static ipv4 address instead? I'm not sure how this all works. I'm new to ipv6.
It is definitely possible - you don't have to change much, you just need to update the DNS entries for your mailserver to point to that IPv6 address.
But whether you really want to do it, is another question... there are still tons of mailservers out there which do not have the means to contact an IPv6 address - none of those domains would be able to send an email to you!
I would rather go with a couple of mailrelays: you have a number of public ipv4 mailservers which do nothing but forwarding emails to the correct server, which stands in a private subnet.
Or you go with an hybrid aproach - mailrelay for ipv4 and directly accessible via IPv6. But if you use IPv4, I would really recommend using a static IP.