Hello,
Years ago we had everyone use their own Domain name with the appended "mail" as their sending and receiving email server (mail.domainName.com).

As time went on we moved to a secure SSL installed on a single domain name (mail.sgdesign.net  IP:  *.97 ) and require everyone to use that for sending and receiving of mails.

Recently we made a change for Reverse DNS and some other settings to assure mail delivery based on other services complaints (Craigslist). This identified that we were using 2 IP addresses (one from a prior server (*.100) as we migrated to our latest server (*.97) ). But this caused problems with the higher IP # being tied to the primary domain server and failing a proper match to mail.sgdesign.net. I removed ties to the older IP and made our Smartermail installation target one specific IP address (*.97).

This solved most of our problems. But we now have some customers still using their own domains for sending and receiving. This causes problems as their DNS points to the older ip (*.100). Note I am changing each customer their DNS to *.97 as these are discovered.

Question: as an MX Record, should I point all domains to mail.sgdesign.net rather than the current mail.domainName.com ? This seems to be a solution to force the redirection of mail to the prior domain and help those customers that have a hard time making settings changes on their devices. Just not sure if this is a good practice.

Question2: For each Domain in Smartermail, should I change their Host Name to mail.sgdesign.net rather than each customers domainName.com which is the current setting?

It seems like there are two solutions to redirect peoples sending and receiving servers without them needing to make changes. I'm just not sure of the ramifications of these changes.

What is the best practice for these settings?