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The reverse DNS resolution (configured as a PTR record) is the association of a domain name with a specific IP address. The DNS / PTR reverse resolution mechanism standards are described in the following RFCs: RFC1033 and RFC1912 Section 2.1
The best practices for servers are to have a PTR record associated with each IP address used to send emails. The domain provided in the reverse DNS belongs to the responsible parties and usually has a website set up with the appropriate contact information for the domain.
** The domain provided in the PTR record of the reverse DNS requires a valid A record (domain or subdomain) that resolves to the server's IP address. **
If your server has more than one IP address, please make sure that all of them have their corresponding PTR registration and (not just the first one).
It is also recommended to configure the domain for the SMTP banner of the mail service to maintain consistency.
Example of a reverse DNS configuration:
mail1.client_domain.com or server1.client_domain.com
* How to verify the PTR record of your server's IP: *
You can use the *host* command, for example if the IP of your server
# host ww.xx.yy.zz
zz.yy.xx.ww.in-addr.arpa domaine name pointer server1.client_domain.com.
However, sometimes there are concepts that can escape us, or which we do not know exactly how they work or what they are for. With this entry we will try to explain, in a simple way, the operation and utility of the inverses associated with IP addresses.
As we know, an IP can be assigned thanks to DNS servers, different names as if it were a phone book. We also know that machines communicate with each other through IP addresses. For people these numbers are complicated to memorize and that is why there is the DNS, which is responsible for associating a name with an IP address, making current Internet use easier. It is easier to remember *seotools.la* than 220.127.116.11, for example.
Now, if we talk about PTR records, their functionality is different. Just as the DNS associates one or more names with a single IP address, the PTR associates a single IP with a single name.
What purpose or uses can this have? The uses of the inverse are very varied, but here we are going to talk about the most common one on a server, which its use to verify the sender of the emails. As an example we will use the domain unelink.es.
Suppose we have configured in our DNS a type A record called *server.seotools.la* that points to IP 18.104.22.168. With this we get that by using the name *server.unelink.es* the DNS redirects us to 22.214.171.124.
But what happens when we send an email from *server.unelink.es*? This is where the reverse takes center stage.
When sending an email from *server.unelink.es* the email header contains, by default, the name *server.unelink.es* (the header is the documentation used by the servers to know the senders and other additional data of the email origin).