Deliverability Glossary


A Record

These records are used to point a domain or subdomain to an IP address. There may be multiple A Records but they are only able to take an IP address as the value. You can point the same domain/subdomain to multiple IP addresses by adding A Records with the same name but different IP addresses for the value.

Example A Record for a mail server:


Host name: mail



CNAME stands for Canonical Name. It points to a host name and not an IP address (so different from an A Record). For example, if we wanted to point to it would be better to do this with a CNAME record. If you have multiple subdomains, you can create multiple CNAME records pointing to the same A Record. That way if you ever change servers and the IP address changes, you will only need to change one A Record and the CNAME records will not need to be changed.


DKIM stands for DomainKeys Identified Mail. It was designed to help ISPs prevent malicious email senders like phishers/spoofers who were sending emails to recipients by saying they are from a trusted brand (think PayPal, Amazon or eBay schemes). It works by adding a digital signature to your email message that validates your domain name when an ESP like Gmail receives it. DKIM’s main purpose is to verify sender identity.


DMARC stands for Domain-based Message Authentication, Reporting and Conformance. Basically, the DMARC policy associated with an email tells an ISP where to place an email based on the SPF and DKIM results. SPF and DKIM must be implemented before a DMARC policy is put in place. DMARC records standardize what happens to your sent mail if the SPF and DKIM authentications fail from the receiving party. DMARC removes guesswork from the receiver’s handling of these failed messages, limiting or eliminating the user’s exposure to potentially fraudulent & harmful messages.


This is the web address that users type into their browser, i.e. Domains are resolved to the IP addresses computers use to connect to the internet.


Behind every email message there are settings that tell the mailbox provider  - like Gmail or Hotmail - who you are and if your messages can be trusted. These settings are your email domain's DNS records. If these settings don't align, mailbox providers are likely to block your messages from getting delivered because you look suspect.

DNS stands for Domain Name System. This system is essentially the "phone book of the Web". When you update your DNS records, you can consider this the equivalent of updating your address in the web's phonebook so that it's possible to verify who you are when you send email. Examples of DNS records include, MX, SPF, DMARC, DKIM etc.


Internet Message Access Protocol (IMAP). This is the Internet standard protocol used by email clients to retrieve email messages on a server without having to download them to your local hard drive. Doing this allows you to be be able to retrieve emails from multiple computers. This is widely used by most email service providers. 

IP Address

The Internet Protocol (IP) address is a unique address that identifies other devices and computers on a network. There are two IP addressing standards IPv4 and IPv6. IPv4 which is most widely used consists of a group of four numbers, each between 0 and 255. For email purposes, a single IP address can be used or an IP range or pool can be used with multiple domains. In the latter case, the reputation of the IP is based on the overall performance of all senders who use it.

MX Record

An MX-record (Mail eXchange-record) contains the mail server that is responsible for accepting emails on behalf of the domain.

An example of an MX-record:



Priority: 10

All emails sent to will be sent to the mail server with the IP address


Simple Mail Transfer Protocol (SMTP). This is the protocol for sending email over the Internet. Email clients use SMTP to send messages to a mail server and that mail server uses SMTP to send that message to the correct receiving mail server. Together, SMTP is a set of commands and rules that authenticate and direct the transfer of electronic mail. If you ever view the original code behind the sleek email you create, you’ll see the commands and instructions that SMTP uses to get your email into the inbox of your recipients.


When you start sending emails through a ESP like Klaviyo, you will be placed on a certain sending IP address that is associated with that ESP. This will raise a red flag for mailbox providers unless there is some setting that tells them this sending IP is allowed to send mail on your behalf. This is where the SPF record comes in as a simple email-validation system.

A basic SPF record:

v=spf1 ~all

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