I want to configure reverse DNS for all the domains (about 100 domains) on same IP.

I want to do this becuase mail sent problem to differnet ISPs. and every one tells that the reason is because domains/mail server are not configured with reverse ip.

my question is,

How i can configure

mail.domain1.com
mail.domain2.com
.
.
.
mail.domain100.com

for reverse lookup, as they are on same IP.

Here is how my dns records are

mail.domain1.com - A - 123.123.123.123
domain1.com - MX - mail.domain1.com

and so on for all 100 domains.

I believe Reverse DNS only can resolve to one domain host name. Basically what happens is that the simple will track back the IP address and see where it resolve to. It is impossible to resolve to more than one domain name.

Yes, this is where i was confused. So i cant have reverse dns for all the domains on single IP, then how the mail servers for each of domain will communicate properly?

On your server, you are only running one mail server and you are not running 100 mail servers on your machine. When it does a reverse DNS, it will reverse to your mail server IP address which is usually your first IP address. Basically as long as it can reverse back to something and not some non-functional IP address or hostname, the recipient mail server would not complain.

Ok, i am clear on this now. thx.

I want my customers to use

mail.client-domain.com

and not

mail.hosting-provider.com

as mail server.

can this be done using cnames.

mail.hosting-providers > cname > mail.client-domain.com

As far as I understand, on a virtual hosting environment it is not possible. You can however get that done if you have a dedicated server running that specific mail server for that client.

However, it may be possible that your mail server is configured to support what you need but I have not encountered any as yet.

Eddy is mostly right, typically, you would only want 1 PTR record per ip address, and the mailserver will always respond with your server's hostname (or whatever is configured in the config file). However, your clients can still use mail.theirdomain.com in their e-mail settings, as long as their mail.theirdomain.com A/CNAME record is pointing to your server.

One of the things I noticed about our plesk install was that it defaulted to adding new ptr records for every domain regardless of whether they were on a dedicated or shared ip. It seems like a rdns would pull a different domain each time from the list of domains on that ip.

Something else I noticed is that retrieving mail was no problem with a cname/alias, but we've encountered issues with sending mail if mail was sent through a non-server name. Sometimes the recipient wouldn't get the mail. Probably due to the dns being different than the rdns. They'd almost always get the mail if we used the servername as the sending mail server instead of the cname/alias.

We do not delegate RDNS entries, so the plesk entries will not get returned.