I currently have an SBS2011 running domain1.com in native mode (i.e. mx records domain1.com->public IP, ptr -> domain1.com) and I have another two domains which I've added as authoritive domains and use SBS POP3 connector to get email for them.
Lately one of the domains has been losing email and I want to make it native with the current host as a backup using mx records. To do this I've thought of the following:
1. mx records domain2.com -> public IP priority 0
mx records domain2.com -> current host priority 100
2. Change current host to act as backup in case public IP goes down and forward email to it once it comes back up.
3. Make PTR changes.
Now my main issues are 2 and 3. Will I need to use cpanel to create the exchange email accounts in the current host or will it keep the email in a general store and send them to the correct recipients once the public IP comes back on. And will I need to make any changes to PTR? Some say yes others just say that I need to make changes to the SPF to allow sending from public IP. Will multiple PTR pointing to one public IP mess things up?