Table of Contents

Email Marketing Terms Glossary

SMTP, spoofing, DKIM, snowshoeing, Honey Pot…confused yet? The email marketing industry is full of terms and acronyms that can seem quite confusing. We compiled a list of more than 135 common email marketing and deliverability terms to reference for email newbies and veterans alike!


A Record

A DNS entry, an A record maps a domain name to the IP address (IPv4) of the computer hosting the domain. Simply put, an A record is used to find the IP address of a computer connected to the internet from a name.

A/B Split

A testing tactic by which two variations of the same email are sent against each other, to measure which one generates higher performance. Results can measure against opens, clicks, or other KPIs. Also referred to as split testing.

Above the Fold

Refers to the part of an email message visible without having to scroll. Content and CTA (call to action) visible in this section is considered more valuable, as the subscriber sees this area first without having to scroll. The fold can be affected by various browsers, devices, mail clients, headers, and screen size. Also referred to as “above the scroll.”


An email marketing advertising model where a company pays compensation to third-party publishers to generate traffic or leads to the company’s products and services.


An email alias is simply a forwarding email address that can contain multiple individual recipients. Example would be, which includes all active 250ok employees.

Application Program Interface (API)

How a program (application) accesses another to transmit data. A client may have an API connection to load database information to an email vendor automatically and receive data back from the email.

Asynchronous Bounce

An email bounce occurring after the Simple Mail Transfer Protocol (SMTP) has ended and is returned to the sender. Opposite of synchronous bounce. Also referred to as “async bounce.”


An additional file accompanies an email message as an “attachment,” but is not included in the actual HTML or body of the email itself. Examples include a word, text, video, PDF, PPT, graphic or other file format. Attachments are risky to include in email marketing as they appear suspicious and a normal vehicle spammers leverage to delivery malware or viruses. ISPs often filter or block attachments in bulk email.


Refers to a collection of techniques designed to verify the identity of an email sender, confirming they are who they claim to be. Email authentication is primarily used to thwart suspicious mail such as phishing and spoofing, and to protect end subscribers from abuse. Most common authentication protocols include SPF, DKIM, and DMARC.



Business-to-business marketing. Example: Kohl’s emailing 250ok.


Business-to-consumer marketing. Example: Kohl’s emailing Joe Smith.


Brand Indicators for Message Identification. An industry standardization effort providing brands the ability to have their company’s logo display in various mail clients to increase brand impressions and encourage the adoption of DMARC and authentication alignment. Currently in beta trials with Oath as of 2018.


A list containing known domains or IP addresses of emailers suspected of sending spam or serving as sources of spam. Many ISPs and mailbox providers use blacklists to reject or bulk inbound email, either at the server level or before it reaches the recipient’s inbox. Also referred to as blocklist.


A term synonymous with sending a large amount of commercial email to a large amount of people. Often implies the same email is sent to a large population, with little to no personalization. Can be viewed as a spammy tactic. Also referred to as “batch-and-blast.”


An action taken by an ISP or mailbox provider preventing your email message from being accepted due to spam, reputation, authentication failures, or other reasons that violate their email and spam policies.


A term referring to when an email is not successfully delivered to your recipients ISP or mailbox provider. Emails can bounce for many reasons, and are often categorized as soft bounces, hard bounces, block bounces, technical bounces, or unknown.

Bounce Handling

The process designed to manage bounced email. A common and customizable feature with ESPs or mail-sending platforms. Essential to have to process and manage bounced emails.

Bounce Message

A string of information sent back to an email sender reporting the message could not be delivered and why. Oftentimes bounce messages are vague and difficult to interpret. Example: “550 5.1.1 The email account that you tried to reach does not exist.” Also referred to as error codes, bounce codes, SMTP errors, or SMTP bounce message.

Bounce Rate

Metric used to measure the amount of mail sent versus the amount of mail bounced and was not successfully delivered. Metric can be bounce-type specific (ex: Hard Bounce Rate) or aggregate against all bounces versus mail sent. This is an inexact number because some systems do not report back to the sender clearly or accurately.

Bulk Folder

The area in a mailbox client or ISP where spam or “spammy” emails are delivered. It is designed for mail that was accepted and delivered, but not deemed worthy of the individual’s inbox. Mail landing in the bulk folder often does not get read or engaged with, and is viewed as a bad result for email and deliverability folks alike. Also known as “spam folder” or “junk folder.”

Bulk Mail

Mail that is commercial in nature, sent in large batches.


Canonical Name (CNAME)

A type of DNS record, the CNAME is can be used to alias one domain name to another.

Call to Action (CTA)

The link or content in an email message serving as the primary recommendation or action suggested to take. Often located above the fold.

Canadian Anti-Spam Legislation (CASL)

Enacted regulations requiring any individuals or organizations sending commercial electronic messages to obtain express content from all Canadian recipients. CASL was created to cut down on spam and, as a result, to reduce the frequency of phishing, viruses, and other malicious threats.


Popular acronym name for the Controlling the Assault of Non-Solicited Pornography and Marketing Act of 2003, U.S. legislation regulating commercial email. Imposes a number of detailed requirements on persons and entities that initiate and send commercial email messages. Violations can result in fines.


A pay-for-play list of senders IPs and/or domains receiving preferential treatment of accepting and inboxing email at various different ISPs taking part in the whitelist. Requires meeting and maintaining certain requirements and standards in order to take part. Most well known whitelist is owned by Return Path, while others include the CSA whitelist (Europe) and SuretyMail.


An email data point in which an individual subscriber receives an email and physically clicks on a link or image within it. Tracked via code in the URL of an image or link. Clicks power many additional click-related metrics such as click-through rate and click-to-open rate

Click-Through Rate

A percentage email metric measuring the number of clicks divided by the total number of emails delivered. Sometimes the number of emails sent is the denominator used. This metric is defined differently between various sending platforms and reporting.

Click-to-Open Rate

A percentage email metric measuring the number of clicks divided by the number of opens.


A spam filter company comprised of spam traps and a network of users as a feedback mechanism to identify and block spam. Cloudmark provides comprehensive security that automatically detects and blocks all forms of inbound and outbound messaging abuse before it can impact subscribers, help desks, networks, and infrastructure. Cloudmark fingerprints all content passing through its network and can lead to mail being blocked or bulked if deemed spammy.

Commercial Email

An email  that’s purpose is to sell, promote, or advertise a product or service. Also known as “bulk mail” or “promotional mail.”


An email-centric metric referring to an individual subscriber marking an email as “spam” in their mail client. By marking an email as spam, it generates a complaint back to the sender indicating the individual considers the mail spam. Complaints are the number of spam button hits generated by all recipients of your email. Complaints are negative and hurt sender reputation.

Complaint Rate

Most often calculated by dividing the number of spam complaints by the number of emails delivered. Note mailbox providers do not always return every unique complaint through the FBL, only a subset. Calculations may vary amongst ESPs.

Confirmation Email

An email acknowledgement of a subscription or information request by a company or organization. Often used to verify an email address used at sign-up or as part of a welcome journey. Typically a trigger-based email sent immediately upon sign-up or request for info.

Confirmed Opt-In

A term referring to a company or organization with verifiably confirmed permission for the email address to be included in their specific mailing list. Facilitated by sending an immediate confirmation email asking for the new email address recipient to “confirm” they wish to join the desired mailing list by clicking a link. This is a best practice to avoid bad email address collection and maintain high list quality. Also referred to as “double opt-in” or “COI.”


See “Permission.”


All the information contained in the email body of a message. Includes all words, images and links.


When an email recipient performs a desired action based on a email message call-to-action you have created. Examples include a subscriber downloading a whitepaper, making a purchase, or signing up for a newsletter.

Conversion rate

A success metric measuring the rate of subscribers who convert to a specific call-to-action or goal of an email campaign.


A technique used in email marketing to greatly increase the number of subscribers in a database by offering opt-in to multiple third-party lists during the sign-up process of a specific company. Not viewed as a best practice. Also referred to as “co-reg” or “coreg.”


An email message copy and any graphics in the HTML.

Customer Relationship Management (CRM)

Technology software that helps a company manage customer relationships in an efficient and organized manner.


Dedicated IP Address

An IP address used only by a singular company or sender. Dedicated IPs are not shared with other senders or organizations. Preferred method of senders who want full management of their IP sender reputation.


The process of removing identical entries or data points from a list or data extension. Most commonly used to remove two or more of the same email addresses on a file or database. Common feature built into many CRMs or data management systems to avoid duplicate entries. Also referred to as “de-duping.”


Refers to the broad subject of a sender’s ability to deliver email into the inbox or desired destination.

Deliverability Rate

Often refers to a sender’s folder placement performance metrics of mail once it is accepted and delivered.  Also referred to as inbox placement rate.

Delivered Email

Number of emails sent minus the number of bounces and filtered messages. Does not reflect the number of emails potentially inboxed versus landing in the spam/junk folder.

Delivery Rate

The rate of number of emails sent that did not bounce. Calculated by the number of emails delivered divided by the number of emails sent.

Denial-of-Service Attack

An organized effort to disrupt email or web service by sending more messages or traffic than a server can handle, shutting it down until the messages stop. A common tactic by malicious groups to disrupt another business. Also referred to as a “list-bomb attack, when used with email.


A company or organization’s name on the internet. Example:

Domain-Based Message Authentication, Reporting & Conformance (DMARC)

An email-validation system designed to detect and prevent email spoofing and phishing. DMARC is built on top of two existing mechanisms, Sender Policy Framework (SPF) and DomainKeys Identified Mail (DKIM) and allows a sender to set a public policy (p=) to dictate what ISPs should do with mail that fails authentication.


A depreciated email authentication system designed by Yahoo to verify the domain name of an email sender and the message integrity. Aspects of DomainKeys, along with parts of Identified Internet Mail, were combined to create DomainKeys Identified Mail (DKIM), which is now widely used.

DomainKeys Identified Mail (DKIM)

Allows an organization take responsibility for a message  in transit. The organization is a handler of the message, either as its originator or as an intermediary. Their reputation is the basis for evaluating whether to trust the message for further handling, such as delivery. Technically, DKIM provides a method for validating a domain name identity associated with a message through cryptographic authentication.

Domain Name System (DNS)

An Internet naming system that translates domain names into IP addresses.  DNS serves as an searchable address book for domain names. Example: Turning into

Dynamic Content

Email content changing from one recipient to the next, according to a set of data extensions or variables a marketer has on its audience base. By using dynamic content, you can ensure a more tailored message is reaching your targeted audience. Dynamic content can reflect past purchases, personas, attributes, suggested items, or other content.


Email Append

A marketing practice taking known customer data (first name, last name, and postal address) and matching it against a vendor’s database to obtain email addresses. Considered a questionable  email collection practice without explicit opt-in permission. Also referred to as “e-append.”

Email Client

The program or software used to read and draft email messages. An email client is the user interface through which an individual has access to their email inbox. Software examples include Outlook 365 or Lotus Notes, and webmail examples include Gmail or Yahoo Mail. Also referred to as a “mail user agent” or “MUA.”

Email Filter

Software or algorithms used to block an inbound email based on the sender, content, reputation, or other variables from being delivered. Filters may be applied at the recipient level, at the email client, the ISP, or a combination.

Email Prefix

The portion of the email address to the left of the @ sign. Also referred to as the “local” part of an email address.

Email Service Provider (ESP)

The name of a company or platform sending email on behalf of their clients. ESPs can vary in size and scale, with some only serving as an MTA engine to deploy mail, while other ESPs offer full marketing suite and campaign services. Examples include SendGrid, Salesforce Marketing Cloud, and MailChimp.


A subscriber-based measurement of how engaged subscribers are with your email program. Engagement is a broad term encompassing how likely subscribers are to open your email, time spent reading emails, clicking, replying, foldering, and other positive explicit actions. Engagement is king with many filtering decisions, as it is a very strong signal from actual subscribers about whether or not the mail is legitimate and should be placed in the inbox.

Explicit Consent

An action taken by an email subscriber to manually opt-in and provide permission to a join a marketer’s email program. An example of explicit consent is requiring a subscriber to click a checkbox to consent to receive an email when completing a sign up form. This is considered the safest option to collect permission and an opt-in from a new email subscriber.


False Positive

A legitimate message mistakenly rejected or filtered as spam, either by an ISP or a recipient’s anti-spam program.

Feedback Loop (FBL)

A service offered by some mailbox providers that shares reports back to senders when individual recipients hit “this is spam” on an email in their mailbox. A FBL offers senders insight into how often subscribers are reporting their mail as spam. Senders should always remove subscribers who have complained after they receive a FBL report of the complaint from the mailbox provider. FBLs are free to register for, and are domain- or IP-based. Not all mailbox providers offer a traditional FBL, Gmail being the most notable.


An area at the bottom of an email message that often contains boilerplate information and is consistent across each email. An email’s footer usually contains contact information, company’s postal address, preference center, unsubscribe links, and privacy policy.

Friendly From

The portion of the email address displayed in most, though not all, email clients or MUA in place of, or in addition to, the email address. Friendly froms can be customized and changed, whereas the sender’s actual from address and domain typically do not. An example: “Your Friends at 250ok.” Also referred to as “display name.”


General Data Protection Regulation (GDPR)

Instituted on May 25, 2018, it replaces the EU Data Protection Directive adopted in 1995. The primary purpose of the GDPR is to protect the personal data of residents of countries within the European Union (EU).

Google Postmaster Tools (GPT)

Google’s web-based set of free tools designed to provide senders and deliverability professionals insights into various reputation and data metrics for a sender, based on domain. GPT provides domain/IP reputation, spam rates, authentication info, encryption, and more based off a sender’s domain.


A term used to describe opt-in, permission-based email an individual does not routinely engage with and may not want. It differs from spam in that the recipient consented to it, and its name derives from being between spam and non-spam.


A method of defending email users against spam.  A server using greylisting will “temporarily reject” any email from an IP it does not recognize. If the mail is legitimate, the originating server will try again after a delay based on their retry policy, and if sufficient time has elapsed, the email will be accepted. Most spam is not sent using RC-compliant MTAs and will fail to retry the mail, preventing it from being delivered.


Hard Bounce

Message sent to an invalid, malformed, or nonexistent email address due to a permanent error and can not be delivered. Often times indicated by a 5xx series bounce error.


Lines identifying particular routing information of an email message, including the sender, recipient, date subject, authentication, and SMTP relays, to name a few.  Headers are found in a delivered email by viewing source or viewing original in the mail client.

Honeypot Spam Trap

A nickname for a  spam trap email address that is created by an ISP or mailbox provider for the sole purpose of catching spammers. These traps never sign up for mail and are spread out on the internet, waiting to be scraped or harvested by spammers. These are the most severe types of spam traps. Also referred to as “pristine” spam traps.

Hypertext Markup Language (HTML)

A standardized system for tagging text files to achieve font, color, graphic, and hyperlink effects on the internet and in email design.


Internet Message Access Protocol (IMAP)

A standard protocol for accessing email from a server.

Implicit Consent

When an individual provides his or her email address during a business transaction or communication, but does not necessarily opt-in specifically for email. An example is a pre-selected checkbox, or requiring an email address as a required field to download an asset but not implying what it will be used for. Implied consent is not considered best practice.

Inactive Subscriber

A term used to describe an individual subscriber who has not opened or clicked an email for a long period of time. Also referred to as “non-engaged subscribers,” “dormant subscribers,” or “non-responders.”


Often refers to the physical hardware or components needed to send email, including the MTA, IPs, domains, and SMTP. Definitions vary.

IP Address

A unique set of numbers assigned to each device connected to the internet. There are two primary types of IP addresses for email senders; dedicated and shared. Example: See unique definitions for both types.

Internet Service Provider (ISP)

Refers to companies offering internet access as well as webmail to consumers. Oftentimes the term “ISPs” is used to describe all mail clients in general. Examples: AOL, EarthLink, Comcast, Verizon, ATT, etc.



Refers to a list or segment of email address to which you are sending your email message.

List Hygiene

The process of routinely maintaining an email list and parsing out hard bounces, unsubscribes, and spam complainers to maintain a clean and updated list. Aides deliverability. Also referred to as “data hygiene.”

List Rental

Tactic in which an email marketer pays a third party to send to their list to increase email reach. Viewed as a negative tactic targeting subscribers who have not explicitly opted-in for your mail program.

List Unsubscribe

An optional custom header addition allowing recipients to see a more conspicuous unsubscribe link in their mail client. Can be either HTTPS or MailTo:  although the MailTo: is more prominent. List-unsubscribe is currently being used by Gmail,, Yahoo, and on Apple’s iOS native mail client.


Mail Bombing

A malicious in nature attempt to shut down a mail server by sending more messages than it can handle in a short period of time. Also referred to as list bombing.

Mailbox Provider (MBP)

Term used to describe any company offering email hosting, but not internet services, per se. Often the term “ISPs” and “MBPs” are used interchangeably and definitions vary. MBPs include ISPs, as it is more of a generic “catch-all” term.

Multipurpose Internet Mail Extension (MIME)

An extension of the original Internet email standard allowing users to exchange text, audio, or visual files.

Mail Transfer Agent (MTA)

Service application responsible for forwarding or relaying electronic mail messages from senders to recipients (or to relay sites) and stores incoming email.

Mail User Agent (MUA)

See email client.

Multi-Part MIME

Bundles together a simplified plain text version of your email along with the HTML version. Most mail clients supporting this format will display the HTML version, but mail clients that can’t will show the text version instead.

Mail Exchange (MX) Record

A record type located in a domain’s DNS. Dictates where mail should be routed with SMTP.



Oath is a subsidiary of Verizon Communications serving as the umbrella company of its digital content subdivisions, including AOL and Yahoo. Verizon acquired AOL on June 23, 2015, and Yahoo’s operating business on June 13, 2017. Oath now makes up Yahoo, AOL, and Verizon mail.

Open Rate

The percentage of emails opened versus the number of emails delivered.

Open Relay

An SMTP email server allowing outside parties to relay email messages through their server and on to their intended recipients. Often exploited by spammers and hackers.


A cornerstone of permission-based email marketing, opt-in is the term used when an individual provides explicit consent to join your email marketing program.


The action of removing one’s self from a mailing list. Also referred to as “unsubscribing.”


Panel Data

Panel data is a term used to describe the collection of data from end-user mailboxes that have installed free email applications in exchange for sharing of aggregate, pseudonymous data. Panel data originates from actual email subscribers who are a part of a sender’s database and have opted-in to one of these free email applications or webmail plugins. The methods by which they inform their users of how data is derived and used is highly questionable.


The implicit approval given when a person actively requests to have their own email address added to a list.


The practice of sending fraudulent emails purporting to be from reputable companies in order to induce individuals to reveal personal information, such as passwords and credit card numbers.


A term referring to a team of individuals who monitor abuse, complaints, and remediation requests at select ISPs or mailbox providers.

Post Office Protocol (POP)

A protocol used to retrieve email from a mail server. Most email clients use either the POP or the newer IMAP protocol.

Pristine Spam Traps

See “honeypot spam traps.”

Preference Center

A landing page providing an email subscriber a centralized and easy way to manage their email preferences, including cadence, content, and volume.


Rate Limiting

See “throttling.”

Recycled Spam Traps

A type of spam trap email address that once belonged to a real subscriber, but was converted into a spam trap after the email address was abandoned or unused for a long period of time. ISPs and mailbox providers will return unknown SMTP bounce errors to a sender when addresses are abandoned as a precursor to recycling an address into a trap.

Reply-To Address

The email address receiving replies from subscribers who respond to a marketing email. This address is often masked when clicking reply, and the actual destination email address of replies is hidden. It can also be different than the from email address. Best practice is to have this inbox or alias monitored to manage any replies from subscribers needing action.


A measurement of a sender’s identity or standing, comprised of thousands of signals and data points over time. Mailbox providers and ISPs each measure a sender’s reputation in their own way. Reputation is associated with a sender’s IPs and domains. Also referred to as “sender reputation” or “sending reputation.”

Return Path Address

Refers to the email address a message actually originated from, as opposed to the “friendly from” address. It is also the address to which any bounces are sent back. Also referred to as the “bounce address,” “envelope from,” or “envelope address.”

Reverse DNS

A reverse DNS lookup is the process of looking up and translating an IP address into a domain name. The opposite or “reverse” of a DNS lookup, which translates a domain name into an IP address.  Also referred to as “rDNS.”



Seeds are a collection of email addresses used to test rendering, delivery, and inbox placement of emails. Seeds can be personal test email accounts, or select vendors offer a range of seed lists covering domains all over the globe for a scalable way to test delivery and inbox placement.


A smaller list from a sender’s overall database built upon specific attributes or data points such as open history, geography, buying behavior, engagement, or other variables. Also refers to the action of creating multiple smaller lists  to target for specific campaigns.

Sender Policy Framework (SPF)

A protocol used to eliminate email forgeries. A line of code called an SPF record is placed in a sender’s Domain Name Server information. The incoming mail server can verify a sender by reading the SPF record before allowing a message through.


A program or computer system that stores and distributes email from one mailbox to another, or relays email from one server to another in a network.

Shared IP

An IP address used for sending by more than one sender at a time. Less ideal than a sender using their own dedicated IP address, as senders leveraging shared IPs have little control over their IP sender reputation, as its shared with numerous other senders. Some ESPs offer shared IP pools, with multiple clients sending from multiple shared IPs. Often a more cost effective option when selecting an IP.

Simple Mail Transfer Protocol (SMTP)

The most common protocol for sending email messages between email servers. Defined by a set of rules regarding the interaction between a program sending email and a program receiving email, including RFC 821 and RFC 5321.

Smart Network Data Service (SNDS)

A free web-based service from Microsoft providing high-level reputation information, spam rates, spam trap hits, and volume for a sender’s IP address.


A technique used by spammers to spread spam output across many IPs and domains in order to dilute reputation metrics and evade filters.

Soft Bounce

A type of email bounce resulting from a temporary failure in delivery of an email message caused by the recipient’s server or mailbox. The email might be held at the recipient’s server and delivered later, or the sender’s email program may attempt to deliver it again. Often indicated by a 4xx series bounce error.

Spam and Open Relay Blocking System (SORBS)

Owned and operated by Proofpoint, Inc., providing free access to its DNS-based Block List (DNSBL) to effectively block email from more than 12 million host servers known to disseminate spam, phishing attacks, and other forms of malicious email. SORBS is a common blocklist many senders hit, but is a low impact blocklist.


The popular name for unsolicited commercial email. However, the definition of spam has evolved over the years to include any mail that is unwanted versus wanted.


A common spam filter using a variety of spam detection techniques, including DNS-based spam detection, content screening, and authentication checks to score emails. SpamAssassin runs these tests to calculate an aggregate score that can be used to determine whether or not a message is spam. The popular choice among those employing SpamAssassin is to mark anything with a score of “5” or more as spam.


An email spam reporting service, allowing recipients of unsolicited bulk or commercial email to report IP addresses found by SpamCop’s analysis to be senders of spam to the abuse reporting addresses of those IP addresses. Many ISPs check the IP addresses of incoming email against SpamCop’s records to determine whether or not the address has been blacklisted due to spam complaints.


One of the more impactful and globally known anti-spam organizations. Based in London, Switzerland, and  Geneva, the non-profit organization tracks email spammers and spam-related activities. The Spamhaus project is responsible for compiling several widely used anti-spam blacklists and blocklists.


The malicious act of falsifying the sender email address to make it appear as if an email message came from somewhere else.

Sunset Policy

A term referring to the defined criteria when an email marketer considers an email address no longer active and will suppress it in the future from commercial emails. Usually, a sunset policy is defined by a length of time when an email address has shown no engagement.

Spam Uniform Resource Identifier Real-Time Block List (SURBL)

A lists of websites that have appeared in unsolicited messages. Unlike most lists, SURBLs are not lists of message senders.

Suppression File

A list of email addresses you have removed from your regular mailing lists, either because they have opted out or unsubscribed from your mail program or other reasons not to receive commercial emails. Required per CAN-SPAM.



Refers to a webmail client’s interface that offers multiple inbox tabs instead of a singular primary inbox. Most notable example is Gmail’s tabbed inbox interface, which offers a Promotions tab, Social tab, Primary tab, and others that can be customized in settings. Also referred to as tabbed interface or inbox tabs.


The practice of regulating how many email messages are sent over the course of a defined time period. Many ESPs offer throttling functionality within their platform. Important to leverage when sending large amounts of volume outside normal ranges as some mailbox providers will defer messages if they receive too many at once.

Transactional Email

An email classification type, opposite of commercial email, designated for mail that is transactional in nature. Defined by CAN-SPAM as “facilitating, completing, or confirming a previously agreed upon transaction.” Examples would be password resets, receipts, itineraries, or privacy policy updates. Does not require an unsubscribe link or postal address.

Transient Bounce

See ”soft bounce.”


Unsolicited Commercial Email (UCE)

Spam or junk mail.


An IP-based spam blacklist primarily used in Europe to catch and block spam and abuse. Usually low impact to delivery when listed.

Unique Open Rate

The percentage of unique emails opened versus the number of emails delivered. A single subscriber opening an email multiple times would only count as one unique open.


The act of requesting to be removed from a marketer’s email program or newsletter. Facilitated by clicking the unsubscribe link or requesting manually to be removed to by the sender. Unsubscribes do not negatively impact sender reputation like spam complaints do.



A pivotal period of establishing a sender’s identity and reputation on new IP(s) and/or domain(s). The term refers to the period of time where senders must prove themselves as legitimate senders when sending off new IPs/domains to prevent ISPs and mailbox providers from bulking or blocking their emails. Requires a slow ramp of volume to highly engaged subscribers to help bolster positive reputation for up to six weeks.


A publicly available and widely used internet record listing identifying who owns a domain and how to get in contact with them.



A customer addition into a header of an email that serves a specific purpose. Examples include campaign-ID, company-ID, or subscriber-ID.