Question about assigned ip to reseller and then email and rDNS/PTR config

[Richard G]

I'm just curious about something. I will use example names and ip's to make life easy, so don't treat it as LAN ip's.

Suppose you have server with hostname server.yourdomain.com and ip address 192.168.0.10 with existing rDNS/PTR records and some domains which send mail and all works fine.

Now you get a reseller and he want's his own ip and he also wants to send mail via his own ip, he does not want that by his mail or any other way, it can be discovered that he is on the same server as yourdomain.com.

So the reseller get's ip 192.168.0.50 and had resellerdomain.com as domain.
I know in directadmin.conf the setting add_domain_to_domainips=1 is required to do this.

If I'm correct then Directadmin takes care of most things like the /etc/virtual/domainips and helo_data.

But if one does not wants to get his mail blocked, one needs a rDNS/PTR record. But you can only have one hostname.
So how does the rDNS/PTR work in this case?
Does DA create a /etc/virtual/helo_data with 192.168.0.50:mail.resellerdomain.com and is the PTR record to bepointed to mail.resellerdomain.com then?
Or how does this part work.

And even more.
Suppose this reseller also has users and wants all his users also to make use of that one ip. Probably not an issue, but if the PTR records is pointing to mail.resellerdomain.com would that be good?

And last question.
If I now telnet to Exim on the main ip address then I will get an answer from Exim like "220 server.yourdomain.com ESMTP" etc. but what if I telnet to the assigned ip, will Exim answer another way, maybe with the helo_data or will it still answer the same as with the main ip?

Just wondering about these things as I've never used it.
Not planning either but I'm just curious.

 

[Zhenyapan]

As I see - it's enough just to have valid (resolvable) PTR/rDNS no matter which domain it, enough that this exact sending IP has rDNS and domain linked resolves back to this IP.
I'm using for 192.168.0.50 like srv050.hostname.com to easier find which IP it about directly from name.

 

[Richard G]

I'm using for 192.168.0.50 like srv050.hostname.com to easier find which IP it about directly from name.

As far as I know from RFC a correct rDNS/PTR needs to point to the correct FQDN hostname the MTA is answering with.
So you say you should some record of in my example resellerdomain.com as rDNs/PTR?

Still then my question remains how the Exim will answer on connect, because if the reseller does not want that to be the fqdn name of the server/vps then I wonder if that is possible.