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For my exchange i need to create PTR record for many domains and assign it to single IP.

like :

mail.x.com assign to 51.51.51.51

mail.y.com assign to 51.51.51.51

mail.z.com assign to 51.51.51.51

I request that to ISP but i ask and need confirm there is any technical limitations and risks regarding assigning multiple domain names for single IP.

test0test
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2 Answers2

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Your question is wrong. A PTR record is typiclly used to convert an IP address back to a domain name. It is important that servers have a PTR record, but a PTR record can only point to a single (sub)domain.

You are more likely interested in MX, A and/or CNAME records, each of which could be relevant to setting up DNS for email - with MX being the only required one.

There is no problem pointing as many domains to an IP address using A records (or indirectly using CNAME or MX records - which are not IP addresses).

In reality, to get mail flowing to 51.51.51.51 you need the following -

  • An "A" record for mail.X.com pointing to 51.51.51.51. (You can optionally have an "A" record for each mail.(any).com record, but it is not required)

  • An "MX" record for each X.com which points to either mail.X.com or mail.(any).com

The risks of assigning multiple domains to a single IP for mail are minimal, but you do need to be aware of the reputation of the mail server, and if a lot of domains are able to relay email through that server, if one of them starts sending spam, the server could get blacklisted resulting in difficulty sending for all other users of the mail server.

davidgo
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@davidgo explained you everything technically correctly, but I afraid you didn't get the point.

Let start with this one:

I request that to ISP but i ask and need confirm there is any technical limitations and risks regarding assigning multiple domain names for single IP.

Technical limitation - No.
Risk - Yes.

Assume a situation, - you driving a car and policeman stop you and ask you for your driver license. What would you expect if you give to policeman 3 driver's licenses with your photo on each of them, but each of them has different last names ?

In your situation, when you have a single IP address and multiple domains that need to be served from the same IP, you need to setup a single SMTP server, assume it would be: mx.main.com

In DNS you should set forward and reverse PTR record for mx.main.com only, then other domains will simply use it as trusted sender. All you need to do, it is set their MX record to point to mx.main.com as

abc.com  MX: mx.main.com
zxc.com  MX: mx.main.com
...
yyy.com  MX: mx.main.com
Alex
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