Deliverability glossary

You will learn

The glossary below defines common deliverability terms and acronyms used in Klaviyo offerings.

A

A records: A records, short for address records, map a domain name to an IPv4 address, such as the address of a web or mail server. You manage these records with the service that hosts your DNS.

Allowlist: A list of items, such as IP addresses, domain names, URLs, or usernames that are allowed access to a certain system protocol. This is also known as a whitelist.

B

BIMI: BIMI stands for Brand Indicators for Message Identification. This is a protocol that allows brands to authenticate the logo shown in inboxes based on sender’s DNS settings.

Block: A block occurs when an incoming email is blocked by the receiving inbox provider. This is typically due to a temporary reason, such as your IP being blocklisted or an issue with the content of the email.

Blocklist: A blocklist is a list of items, such as IP addresses, domain names, URLs, or usernames that are denied access to a certain system protocol. Email blocklists are real-time databases that use criteria to determine if an IP is sending email it considers to be spam. There are blocklists for both IP addresses and domains that can severely impact their reputation and deliverability. This is also known as a blacklist.

Bots: Automated programs that malicious actors use to submit large numbers of sign-ups at once. The submitted email addresses may look legitimate at first. This practice is called list bombing and is a form of cybersecurity attack.

Bounce: When an email is unable to be delivered. There are two types of bounces: hard and soft. Hard and soft bounces occur for different reasons.

Branded sending domain: Branded sending domains (also known as dedicated sending domains) use the domain of a business instead of a shared domain supplied by Klaviyo. This process is also known as whitelabeling. A branded sending domain has a send type that determines the kind of email traffic it carries: marketing, transactional, or service. You can configure one active branded sending domain per send type, and briefly two while a domain is being replaced.

C

CAN-SPAM Act: A US law intended to minimize the sending of unwanted emails, otherwise known as spam. CAN-SPAM “sets the rules for commercial email, establishes requirements for commercial messages, gives recipients the right to have you stop emailing them, and spells out tough penalties for violations.”

CASL: CASL stands for Canada’s anti-spam legislation and is similar to the CAN-SPAM Act in that it regulates the types of emails sent by commercial senders. CASL “protects consumers and businesses from the misuse of digital technology, including spam and other electronic threats. It also aims to help businesses stay competitive in a global, digital marketplace.”

CCPA: CCPA stands for California Consumer Privacy Act. It took effect on January 1, 2020, and governs how businesses handle the personal information of California residents.

Click tracking: The process of recording clicks on links in an email for analytics. Klaviyo uses tracking URLs for the links it tracks. Recipients can see the tracking domain when hovering over a link or when clicking a link within the email.

Clipping: An email is “clipped” by Gmail when its code exceeds Gmail’s size limit, generally 102 KB on desktop. The limit can be lower on mobile devices. When clipping hides the open-tracking pixel, opens may be underreported because the pixel does not load. Moving the tracking pixel to the top of your emails can help track opens when an email is clipped. For more information on clipping and how to prevent it, check out our guide.

CNAME: CNAME is short for canonical name. This can be used to alias one name to another.
A common example is when you have both example.com and www.example.com pointing to the same application and hosted by the same server. In this case, to avoid maintaining two different records, it’s common to create:

• An A record for example.com pointing to the server IP address
• A CNAME record for www.example.com pointing to example.com

As a result, example.com points to the server IP address, and www.example.com points to the same address via example.com. Should the IP address change, you only need to update it in one place. If you edit the A record for example.com, www.example.com automatically inherits the changes.

D

DDoS attack: DDoS stands for distributed denial of service. In a distributed denial-of-service attack (DDoS), the incoming traffic flooding the victim originates from many different sources. This effectively makes it impossible to stop the attack simply by blocking a single source.

A DoS or DDoS attack is analogous to a group of people crowding the entry door of a shop, making it hard for legitimate customers to enter, thus disrupting business.

Dedicated click tracking: Dedicated click tracking allows a customer to display their own domain on click-tracking links as opposed to the default Klaviyo encoding. You need a paid Klaviyo account to configure a dedicated click-tracking domain from your account settings.

Dedicated IP address: A dedicated IP address is an IP address that only one account uses (see also shared IP address).

Deferred: A deferred email means that the email was temporarily rejected by the inbox provider. Klaviyo will retry the message later, but it can still bounce if delivery continues to fail.

Deliverability: Email deliverability is defined as when an email successfully reaches the inbox (including tabbed inboxes, such as Google’s Promotions tab). Placement in the spam folder or a block from the inbox provider indicates a deliverability problem.

Delivery: A delivery occurs when the recipient’s mail server accepts an email. Even if your email was delivered to the spam folder, it still counts as a delivery.

DKIM: DKIM stands for DomainKeys Identified Mail. DKIM is a cryptographic technology created by Cisco and Yahoo that uses a digital signature to associate an email with a sending domain and detect changes to the signed parts of the message in transit. It’s also known as “email signing.” Receiving servers check the signature using a public key published in DNS. For a Klaviyo branded sending domain, the CNAME or NS records generated during setup provide the necessary DKIM authentication.

DMARC: DMARC stands for domain-based message authentication, reporting, and conformance. It checks that an email passes SPF or DKIM authentication and that the authenticated domain aligns with the domain in the From address recipients see. A message passes DMARC when at least 1 of these methods passes with alignment. The domain owner’s DMARC policy requests how receiving servers handle messages that fail, such as monitoring without requesting a delivery change, placing them in spam, or rejecting them. Domain owners can also configure DMARC reports to learn about mail sent using their domain.

DNS: 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 an email. When we talk about a DNS provider, we’re talking about a service that hosts your domain name, like GoDaddy, or Cloudflare, HostGator, SquareSpace, etc.

Domain: A domain is the registered name that emails and images are sent from, like Klaviyo.com or boston.com. The domain name must be registered before you can use it. Every domain name is unique. No two websites can have the same domain name.

Domain reputation: A measure of how inbox providers view a sending domain’s trustworthiness, based on sending practices and infrastructure.

DoS attack: DoS stands for a denial of service. In computing, a DoS attack is a cyber-attack in which the perpetrator seeks to make a machine or network resource unavailable to its intended users by temporarily or indefinitely disrupting services of a host connected to the Internet. Denial of service is typically accomplished by flooding the targeted machine or resource with superfluous requests in an attempt to overload systems and prevent some or all legitimate requests from being fulfilled.

E

Email engagement: Email engagement refers to recipients opening and/or clicking the emails you send them. Email engagement is used by inbox providers to determine whether or not your business is practicing good sending habits.

ESP: ESP stands for email service provider, or a system that you can use to send commercial and transactional emails to your customers. Klaviyo is considered an ESP.

G

GDPR: GDPR stands for the General Data Protection Regulation. It’s an EU law adopted in 2016 that has applied since May 25, 2018. It governs the processing of personal data by organizations established in the EU and can also apply to businesses outside the EU that offer goods or services to people in the EU or monitor their behavior there.

H

Hard bounce: A hard bounce occurs when an email cannot be delivered due to a permanent reason, such as an invalid email address. Klaviyo will automatically suppress any email addresses that have hard bounced.

Header: Also called the email header, this refers to identifying information about email such as the subject line, from address, recipient address, date, and more.

I

Inbox provider: Also called a mailbox provider, this is a service used to manage email correspondence, for example, Outlook, Gmail, and more. These are companies that provide their customers with servers to send, receive, accept, and store email. Some inbox providers attract users because they are free and they advertise their services on every message.

IP address: An IP address is a numerical address that identifies a device or server on a network. In email sending, it identifies the server sending mail on behalf of your domain. Inbox providers check the reputation of the sending IP address.

IP reputation: A measure of how inbox providers view an IP address’ trustworthiness as a sender, based on sending practices and infrastructure.

ISP: ISP stands for Internet service provider. These are organizations that provide services for accessing or using the Internet. Some ISPs also provide email service but may lack some features that are typically offered by providers who focus primarily on email. This includes web-hosted inbox providers, like Verizon, Xfinity, and more.

L

List bombing: List bombing refers to the practice of abusing and attacking email list signup pages by bombarding them with a large number of new email addresses at the same time. At first, it may look like a spike in signups. In reality, it’s a cyber attack.

List cleaning: List cleaning is the process of removing invalid and/or unengaged contacts from your subscriber list. This ensures that you don’t inadvertently email any addresses that will negatively impact your sending reputation.

M

MBP: MBP stands for mailbox provider, also called an inbox provider. This is a service used to manage email correspondence, for example, Outlook, Gmail, and more. These are companies that provide their customers with servers to send, receive, accept, and store email.

MX record: MX record stands for mail exchange record. This specifies the mail server responsible for accepting email messages on behalf of a domain name. It is a resource record in the DNS.

An MX record points to a mail server’s domain name. That name must resolve to an IP address through an A record for IPv4, an AAAA record for IPv6, or both. Other mail servers use this information to find where to deliver email for your domain.

P

Permission pass: A one-time email sent to recipients to verify opt-in permission. It requires that you have already gained verifiable opt-in permission at some point, but perhaps you haven’t seen them engage with your messaging in a long time. Recipients who open and click a CTA within the email to confirm their subscription will remain subscribed, while recipients who don’t click are suppressed or removed from your email list. The latter category of recipients should be engaged through other marketing channels and driven back to your website, where they can resubmit an email signup form to receive future emails.

Phishing: A hacker attempts to fraudulently retrieve a user’s sensitive information by imitating electronic communication from a trusted organization in an automated manner.

Pristine spam trap: A pristine spam trap (PST) is created with the intention of finding people who are sending spam or not following best sending practices. These emails are never used in real-world instances and are brand new addresses, so hitting a PST is likely to cause your IP to be blocklisted or your emails to go to spam. In the eyes of mailbox providers, this means you either purchased a list or do not follow best practices since these addresses are not legitimate and do not open emails.

R

Ramping: Ramping is a process that aids in the overall warming process to become a reputable sender, whether you are using a dedicated or shared IP. It involves starting with smaller email volumes and gradually increasing them over time. When ramping a dedicated IP, this will be part of your overall warming process as it relates to your new infrastructure. Ramping shared IPs involves new customers needing to warm their reputation relative to their new relationship with Klaviyo IPs.

Recycled spam trap: A recycled spam trap (RST) is an address that was used as a real address at some point in the past. It’s common to see RSTs as domains provided by free services, such as @yahoo or @gmail. You may see domains of closed businesses repurchased with the intention of making them RSTs. An out-of-date email doesn’t always become an RST immediately. Some inbox providers may delete the address after no activity -- e.g. if the address stops receiving emails.

S

Send type: A property of a branded sending domain, shown as Email type during setup, that determines what kind of email traffic the domain carries. The 3 send types are marketing (campaigns and promotional flows), transactional (flow messages designated as transactional, such as order confirmations and password resets), and service (support replies sent through Klaviyo Helpdesk, including Customer Agent). An account can have 1 active branded sending domain per send type, and briefly 2 while a domain is being replaced.

Sender reputation: A measure of how inbox providers view an email sender's overall trustworthiness, based on their sending practices and infrastructure. Sender reputation is a key consideration inbox providers use when determining where to place an email (e.g., spam, promotions, primary).

Sending domain: The sending domain is the registered name on the internet (e.g., companyxyz.com). A domain reputation is the sending reputation for the domain name. This can be the subdomain or domain.

Service sending domain: A branded sending domain configured with the "service" send type. Service sending domains carry support replies sent through Klaviyo Helpdesk. Enable inbound email in your Helpdesk email settings before adding a service sending domain.

Shared IP address: An IP address that multiple senders use.

Shared sending domain: Shared sending domains contain a root domain shared among multiple Klaviyo accounts. Klaviyo automatically adds a unique element to sending domains to make it easier for more sophisticated inbox providers like Gmail and Hotmail to identify each sender as different.

Soft bounce: A soft bounce occurs due to a temporary reason, such as the inbox being full or the recipient’s email server being down momentarily. Klaviyo will automatically suppress email addresses that soft bounce 7 consecutive times within 2 years.

Spam: Spam is unsolicited bulk email.

Spam complaint: A spam complaint is recorded in Klaviyo when an email recipient marks one of your emails as spam and their inbox provider reports the complaint to Klaviyo. This is tracked in the analytics of a particular campaign or flow email. Gmail does not report individual spam complaints to Klaviyo. Spam complaints are not tracked when an email simply winds up in the spam folder, but only when someone takes action to mark your email as spam.

Spam trap: A spam trap is an email address, or in some cases, an entire domain, used to capture, collect, and monitor email sent to it​. Spam traps are usually created and managed by ISPs, mailbox providers, mail administrators, and/or other similar groups. The main purpose of spam traps is to collect information about senders to help prevent future spam.

SPF: SPF stands for sender policy framework. An SPF record is a DNS TXT record that identifies the mail servers authorized to send email for a domain. Receiving mail servers check the sending server’s IP address against this record. SPF checks the domain used for the email’s return address, which can differ from the From address recipients see. DMARC checks that the authenticated domain aligns with the visible From address.

Spoofing: Email spoofing means that a phisher has modified the email header of a message so that it appears as if it was sent from someone else. Hackers may use this technique to impersonate an employee of a company, for example, to obtain login credentials, personal data, or other confidential information.

Subdomain: A domain within a parent domain. For example, send.helloworld.com is a subdomain of helloworld.com, and send is the prefix you enter when setting up that sending domain.

Suppress: A suppressed email profile cannot receive marketing emails. Email suppression does not automatically prevent messages through other channels. Profiles suppressed for bounces or invalid email addresses cannot receive transactional emails either. An email profile can become suppressed for reasons including:

• Unsubscribing
• Marking one of your emails as spam
• Hard bouncing
• Soft bouncing 7 times in a row within 2 years
• Being manually suppressed

T

TINS: TINS stands for this is not spam. When recipients recover an email from their spam folder by marking it as “this is not spam,” they let the inbox provider know that they would like to receive these emails.

Transactional sending domain: A branded sending domain configured with the "transactional" send type. Only flow messages that have been designated as transactional can be routed through a transactional sending domain. Campaigns are not eligible.

TXT record: TXT record stands for text record. These hold free form text of any type and are used to verify the authenticity of emails. Historically, they have also been used to contain human-readable information about a server, network, data center, and other accounting information.

A fully qualified domain name may have many TXT records. The most common uses for TXT records are SPF, DK, DKIM, and DMARC.

W

Warming: Warming refers to the process of establishing a good sending reputation when you first start sending emails with Klaviyo. The warming process is especially important if you are sending from a dedicated IP address and/or dedicated sending domain. The exact warming schedule will vary from case to case, but in essence, to warm your sending infrastructure, you will need to turn on high engagement flows, send your first campaigns to highly engaged recipients, closely monitor your engagement, and adjust accordingly.