Which type of DNS Record Identifies an Email Server? (Explained)

Which type of DNS Record Identifies an Email Server?.  Not many of us notice the complex relaying of messages that occurs behind the scenes every time we click “Send” in our email applications. It doesn’t matter if it is a cloud email client like Gmail or a proprietary one like Microsoft Outlook, a relaying of messages from client to server to a recipient is possible in the background thanks to the types of DNS records that identify email servers – which is what we will be talking about in this post.

Which type of DNS Record Identifies an Email Server

 These DNS records are:

    • MX Record
    • A Record
    • AAAA Record
    • CNAME Record
    • TXT Record
    • NS Record
    • SPF Record
    • Caller ID Record
    • SOA Record
    • PTR Record
    • CERT Record

We will have a look at each record in detail. But, for now, let us start from the basics and build up from there.

What is an Email Server?

An email server retrieves, sorts, and sends emails to their intended destinations. It can be considered to be a computer that serves as an electronic post office for email being sent within and without a network.

Types of Email Servers

There are three main types of emails servers:

    • SMTP Servers – Simple Mail Transfer Protocols (SMTP) servers handle outgoing mail.
    • POP3 Servers – Post Office Protocol, version 3 (POP3) servers are used for storing sent and received messages locally, on a user’s PC drive.
    • IMAP – Internet Message Access Protocol (IMAP) servers are used to store copies of messages on the email server. These copies are used to synchronize the mailboxes.

What is a DNS server?

Another important part of the email process is the DNS server – short for Domain Name System server. This is a server that translates domain names to IP addresses and is a large-scale system that contains all the information across all websites on the internet. This makes it possible to change human-readable addresses like “acme.com” to machine-readable IP addresses.

A DNS server also holds information like domain names, hosting, IP addresses, and other registrations. This information is accessed by following instructions stored in DNS records.

What is a DNS record?

Simply put, the DNS records are a set of text files that act as commands to instruct anyone that connects with a server on what to do.

Information stored in the DNS records includes which URLs lead where, what IP address to follow to get to a certain subnet, filters that stop spamming, and even have a TTL or “Time-To-Live” that tells when the server should refresh all of this information.

Needless to say, all domains must have a few DNS records. It allows users to find the specific sites they are looking for when using the domains – including its email servers.

Which type of DNS Record Identifies an Email Server

Ok; let’s dive right in and have a detailed look at each type of DNS record that helps identify email servers:

MX Record

The Mail Exchange (MX) records are DNS records that are necessary for matching emails to the destination address.

The MX record is used to tell the world which mail servers accept incoming mail for a particular domain and where emails sent to the domain should be routed through. An error in configuring this record results in failure of email delivery.

A Record

An A record – the “A” stands for address – is a type of DNS record that points a domain to an IP address of, usually, a website’s hosting provider.

This record allows DNS servers to know the IP address of the website by matching its domain name (acme.com) with its IP address. Anyone looking for acme.com would be directed to this DNS server – or any one of them that has these records.

AAAA Record

An AAAA Record (quad A Record) is another type of DNS Record that points a domain – or its subdomain – to an IPv6 address.

The only difference between an A Record and an AAAA Record is that the former uses corresponding IPv4 addresses while the latter uses IPv6 addresses.

CNAME Record

A Canonical Name or CNAME Record is a record that maps one domain name to another. This is particularly useful when there is more than one service running on a single IP address.

A good use for this record would be when a business has a “WWW” subdomain as an alias to its root domain. The CNAME Record would direct all users typing in “www.acme.com” would be directed to “acme.com” instead.

If the domain has FTP or email services, this record will point people who are looking for the repository or messaging server accordingly.

A CNAME record always points to a domain and never to an IP address.

TXT Record

A text or TXT Record is a resource record in a DNS that allows for the association of arbitrary text with a host or any other asset. It can be used to store human-readable information about servers, networks, hosts, and similar digital assets.

A common use for TXT Records is for email spam prevention. In the example below, a record has been created to help protect Exchange Online email accounts and from spam:

TXT Record for preventing spoofing and spam on Outlook

A TXT Record is also used by domain and hosting companies to help verify users are the actual owners of such digital assets.

NS Record

The NS Record stands for Name Server Record which is the most authoritative DNS server in a region. These records help identify DNS server names, and as a result, ensure the availability of the domain name that is being searched or queried.

Whenever a server – including an email server – is switched to a new hosting service provider, the NS Records need to be updated accordingly.

SPF Record

The Sender Policy Framework or SPF Record is an old record type that was used to verify the identity of the sender of an email message. Today, it is no longer recommended to create this record type.

The SPF record creates a way for other mail servers to verify if an email they receive – claiming to be from the server – is indeed from one of its domain’s IP addresses. This helps prevent email spoofing.

Caller ID Record

The Caller-ID Record too is an older record that performed the functions that the SPF Record does today- albeit in a slightly different way. Here too, the mail servers were able to verify if mail claiming to be from a certain domain, were indeed from one of their IP addresses.

This record type is deemed to be redundant since its tasks are covered by an SPF Record. But, the different ways that they tackle email authentication make it popular with some other fans.

NOTE: You can only use Caller ID and SPF records if messages are delivered by the SMTP protocol.

SOA Record

A Start of Authority or SOA Record provides information about a domain and its corresponding or “authoritative” primary name server of a particular region.

Apart from the Authoritative Name Server for the current DNS Zone this record holds the contact (email) details of the administrator, refresh times, length of time before the server can ask for an update, and TTL times – among other things.

PTR Record

The Pointer or PTR record is a reverse lookup record that maps or resolves an IP address to its corresponding domain or hostname.

Some email servers will refuse to transmit or accept an email that is sent to them without being able to verify the email’s authenticity by doing a reverse lookup. They only accept messages from mail servers that can make a reverse DNS lookup – which a PTR Record refers to.

These records are commonly used for IP addresses on LANs where it makes it easy to look up an IP address to find its corresponding domain on the network.

It is the reverse of the A or AAAA records because a PTR record resolves IPv4 or IPv6 addresses to domain names.

CERT Record

The CERT Record is used to store certificates – to verify the authenticity of both sending and recipient parties – and the related revocation lists (CRLs) which identify certificates that are no longer valid.

These records are also used by systems for email encryption – hence the need for verifying both parties that are at the sending and receiving ends.

Importance of maintaining DNS records for an Email Server

Maintaining DNS records ensures the quick and safe delivery of emails. Without these records, emails would be dropped, bounced back or flagged as spam. Addresses or destination domains would not be found meaning the emails wouldn’t even know where to go.

That is why you need to take care when configuring and maintaining your DNS records. We can help with the configuration and administration of mail servers for complex architectures. Contact us and let us help.

Avatar for Liku Zelleke
Liku Zelleke

Liku Zelleke is a technology blogger who has over two decades experience in the IT industry. He hasn’t looked back since the day, years ago, when he discovered he could combine that experience with his other passion: writing. Today, he writes on topics related to network configuration, optimization, and security for Cloud Infrastructure Services.

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