I am setting up several virtual domains on a single VPS and I'm a little confused about MX records. My desire is for users with email accounts on the various virtually hosted domains to be able to use something like mail.their-virtualdomain.com as incoming and outgoing (smtp) server names when setting up their email client software. This would be opposed to having them use the FQDN of the VPS where the email server is running (say, server1.mycompany.com). Here's what I think so far:
Some people try to use CNAME records for this, and it might even sort of work when communicating with some external email servers. But it's against the RFC and it will fail in some situations. So we don't want to do this.
I think better is the suggestion to make an A record for mail.their-virtualdomain.com with the IP address of the VPS server, and then an MX record using mail.their-virtualdomain.com. I believe this works at least to some extent. But I'm unclear on at least two possible problems here:
1) At least with my VPS host (and I think this is normal) only my FQDN (server1.mycompany.com) gets a PTR record. So I think reverse DNS will only work with the FQDN. Does this mean my goal is impossible because users using mail.their-virtualdomain.com as an outgoing SMTP server will fail reverse DNS checks and thus be more likely to be marked as spam? Or maybe I'm not understanding reverse DNS.
and if 1) isn't a show stopper, then:
2) If users want to connect using SSL for sending and receiving mail, I would have to get an SSL certificate for each virtual domain? (whereas if all users use the FQDN as their mail server then I can just get a single certificate.) I know I can do self signed certs for free, but this doesn't strike me as a bulletproof solution (users might still get warnings that certificate is self signed and not secure?)
I'm guessing other people must have this desire. What do people do? What am I missing? Thanks.