Glossary of Terms



The rate at which recipients open emails from a sender, usually expressed as a percentage. Usage example: “The average open rate of the new email campaign is 40%.”


BIMI (noun)

This stands for Brand Indicators for Message Identification, and if your brand is authenticated, a BIMI is a standard allowing you to display your brand logo with emails sent from your domain. Can sometimes be used to differentiate real brands from knock-offs. Usage example: “Companies that use BIMI can choose the logo displayed in recipients’ inboxes.”

BLOCK (verb)

To reject a message before ever attempting to deliver it to the inbox. Usage example: “She blocked my address.”


A list whose purpose is to track and penalize spam. While most blocklists won’t necessarily affect your email deliverability, there are several blocklists that will affect it. These include Barracuda, SpamHaus, Invaluement, and Proofpoint. Being on these blocklists may mean spam placement and mail rejection by a large portion of your recipient addresses. Usage example: “This blocklist is the reason my bounce rate is so high.”

BOT (noun)

Short for “robot,” a bot is any automated procedure that can be used for mass actions such as voting in online polls. Bots typically impact email deliverability by flooding email forms with fake information, which in turn can result in your email lists being marked as spam due to large-scale illegitimate emails being put into sender lists. Usage example: “I guess most of these new addresses are actually bots.”

BOUNCE (verb)

To fail to deliver to a recipient domain, or to be rejected by a receiving email server. This kind of rejection notice indicates that the email address is either invalid or cannot be accessed. Usage example: “This email bounced, so the contact will never see it.”


The rate at which email messages are not accepted for delivery, usually expressed as a percentage. Usage example: “Our bounce rate for the latest email campaign is 13%.”



The Controlling the Assault of NonSolicited Pornography And Marketing Act sets the rules for commercial email sending in the United States. Visit CANSPAM Act: A Complete Guide for Business for more information. Usage example: “CAN-SPAM laws say you must clearly disclose your message as an advertisement.”

CASL (noun)

Canada’s Anti-Spam Legislation is a Canadian law designed to control and prevent spam. Visit Canada’s Anti-Spam Legislation for details. Usage example: “To be compliant with CASL, senders must obtain consent, provide identification information, and a way to unsubscribe.”

CCPA (noun)

California’s Consumer Privacy Act gives California-based consumers privacy rights and control over personal data. These include the right to opt out of the sale of their personal information. For more information, visit this CCPA overview page. Usage example: “Because of CCPA, these recipients have the right to know what information we’re collecting from the


The rate at which email messages derive clicks divided by the number of times the email was opened. This metric is used to determine the effectiveness of an email’s content. If your click to open rate increases, it means that more people are engaging with the content once they open the message. Usage example: “The click to open rate went up by 20% since we hired the new content writer.”


The rate at which email recipients click a specific link, usually expressed as a percentage. To determine this rate, you would divide the number of people who clicked on the link by the total number of emails delivered. This metric can be helpful in determining a marketing campaign’s success. Usage example: “Our click-through rate is down compared to the last campaign, but I need to figure out why.”


When a full-length email would be too large and is therefore cut short with a “click for more” prompt. Usage example: “This email is clipped, but the users can click on that button to see the email in its entirety.”


Also known as DOI, or double-opt in. A way to confirm that recipients want your email, this process asks recipients to verify a specific email subscription. This verification may be done, for instance, by using a form or clicking a link. Usage example: “We’re getting fewer email bounces since we started doing confirmed opt-in.”

CONSENT (noun and verb)

In this context, when a recipient opts to receive emails from your company, or gives permission to be contacted. Usage example: “These users consent to get our marketing emails.”



A static IP address used to send email on behalf of one unique brand or company. Usage example: “our dedicated IP sends all our content.”


The success — or failure — an email has in reaching a receiver’s inbox. Email deliverability may be influenced by email list quality, email content writing, and various spam markers. Usage example: “There are so many things that could improve our deliverability, I don’t even know where to begin.”

DELIVER (verb)

To reach the servers of your subscribers. The opposite of an email bouncing. Usage example: “90% of our emails were delivered, but we’re still having trouble getting into our subscribers’ inboxes.”

DOMAIN (noun)

Domain names refer to specific internetconnected servers and devices. Domain names can represent different IP addresses and servers. Usage example: “ and have the same domain even though the addresses are different.”


Somewhat like the internet’s own internal telephone book, the DNS converts alphabetic domain names into numeric IP addresses. Usage example: “When I type this URL, the DNS servers know which IP address to send me to.”


The overall health of your domain according to mailbox providers. A number of things can negatively and positively influence domain reputation, including bounce rates, sending history, and spam markers. Usage example: “Our domain reputation seems to have slowly improved over the last 30 days.”



Platforms that send commercial emails on behalf of customers. Examples include MailChip, ActiveCampaign, and Constant Contact. Usage example: “This ESP will send our email campaigns for us.”


How well or poorly your contacts interact with your emails. This can be measured by looking at things like opens and clicks. Usage example: “Good engagement usually translates to good deliverability, since our reputation plays such a strong role in deliverability.”



A regulation of the European Union designed to protect the privacy of its citizens. Addresses the transfer and storage of personal data both within the European Union and out of it. Usage example: “If we’re selling to Europeans, we need to be GDPR-compliant.”


HARD BOUNCE (noun and verb)

A permanent email bounce that occurs when the address or domain doesn’t exist. This type of error may be caused by typos, deleted user accounts, or fake addresses. Usage example: “Hard bounces should be removed from email lists.”

HEADER (noun)

In this context, a header contains certain information identifying, including an email’s sender, recipient, subject, and date. Most of this information is hidden, and only the most relevant information appears to the user. Email marketing laws for some territories stipulate that you must not include incorrect information in header fields in order to trick people into opening your emails. Usage example: “Looking at email headers may help identify why your email wasn’t delivered.”


In this context, an inactive address created to catch spammers. Because these emails aren’t used by real people, if a company sends an email to a honeypot address, it will be flagged. Usage example: “Obviously, this honeypot has never opted in to any email campaign.”



A company that offers internet to personal and business consumers. ISP companies include cable or internet providers like Comcast, AT&T, and Verizon. These providers may also provide email inboxes to their customers. Usage example: “I switched ISPs and my movies stream better now.”

IP (noun)

In this context, IP stands for “Internet Protocol.” Usage example: “Here’s his IP address.”


A unique string of numbers that identifies a computer and is used to distinguish senders and websites. Usage example: “IP addresses help internet-connected computers find each other.”


Where people see their emails. An inbox provider can be an ISP, a webmail account, or an email app. Gmail is one of the most popular inbox providers, but there are many others, such as Outlook and Yahoo Mail. Usage example: “My inbox provider used to be Hotmail, but I switched to Apple.”


Similar to any other kind of email deliverability reputation, this is based on the historic activity of an IP address and how users engage with the mail that comes from it. Usage example: “IP reputation can be either positive or negative.”



The metaphorical cleanliness of your email list, determined by how well you remove inactive or bounced email addresses from your list. Usage example: “Keeping uninterested subscribers on your email list reduces your deliverability rates.”


OPT OUT (verb)

In this context, to decline email communication. Usage example: “This customer opted out by clicking the email’s unsubscribe link, so he’s being added to our exclusion list.”



To send fraudulent emails, often by pretending to be a reputable person or company. The goal of phishing is to obtain the reader’s personal information. Usage example: “If we have too many typos in our email, we’re probably going to look like we’re phishing.”



A type of honeypot. An old email address that is no longer in use and has been repurposed to catch spammers. Usage example: “This address has been inactive for five years, so we should use it as a recycled spam trap.”


A hidden email header indicating where and how bounced emails will be processed. Also called a bounce address or reverse path, this address is separate from your original sending address, and is used for processing bounced messages. Usage example: “Companies can use the return path to park the hundreds of bounce receipts they get from an email campaign.”



A filter that email recipients can create to manage their emails. When companies are added to a user’s safelist, their emails are more likely to be delivered to the user’s inbox. Usage example: “Having a safelist helps ensure recipients won’t miss messages they want.”


The separation of contact lists. MailMonitor recommends splitting lists into active and inactive segments, with active users having opened or interacted with an email in the last 60-90 days. Inactive users would have little to no activity historically. Usage example: “The segmentation of contact lists can help with deliverability.”


A TXT record on your domain that authorizes certain servers to send mail using your domain name. Usage example: “This company can automatically use SPFs on behalf of clients.”


The domain a brand has purchased to use for email marketing. Usage example: “This sending domain will send all our emails.”

SHARED IP (noun)

An IP with many different senders. Usage example: “This shared IP has different people using it simultaneously.”


A method of sending email over the internet. Mail servers use SMTP to send and receive email messages, for instance. Usage example: “One protocol for sending email is called SMTP.”


A simple method whereby a recipient indicates that they wish to receive messages from a particular sender. Usage example: “Single opt in can be done with a form the user fills out or something else.”

SOFT BOUNCE (noun and verb)

An email soft bounces when it cannot be delivered to the recipient due to temporary failures such as a full mailbox or a technical problem. Usage example: “The email bounced, but it was a soft bounce, not a hard bounce.”

SPAM (noun and verb)

Bulk messages sent without the explicit consent of the receiver, and the act of sending those bulk messages. Usage example: “I’m getting spammed with spam.”


A report from an end user flagging an email as spam. This can be done by hitting the “mark as spam” button, for instance. These flags are reported to providers and ESPs. Usage example: “If your spam complaint rate is high, your sender reputation will be low.”


Emails that are routed to spam folders. Usage example: “Spam placement can happen for many reasons, but often has to do with sender reputation and content.”

SPAM TRAP (noun)

A honeypot. An inactive email address that does not belong to a real person, and is used by mailbox providers and blocklist services to catch senders who have poor list hygiene or who aren’t sending to opted in lists. Usage example: “Watch out for spam traps.”


To run an email scam that targets individuals or specific organizations. Unlike standard phishing emails, which are usually sent in bulk to large numbers of people, spear phishing is tailored for a specific target. The attacker will first gather information about the target, such as their name, work, interests, and even personal details. They’ll then craft a personalized email that contains false information, links to malicious websites, or malicious files. Usage example: “The goal of spear phishing is to trick the target into clicking on the malicious link or downloading the malicious file, and thus, giving the attacker access to the target’s computer or personal information.”


A type of scam used by malicious actors to gain access to confidential information. It occurs when someone uses false information, such as a fake phone number, email address, or website URL, to disguise their identity when communicating with victims. Usage example: “Spoofing uses false information to try to get victims to share sensitive information, such as banking details or passwords.


An addition to a domain name that can be used to organize content on a website or direct traffic to a specific page. For example, a subdomain might be “,” where “” is the main domain. Subdomains can be useful for creating a separate page for a specific product or service. Usage example: “Subdomains can be used to isolate mail streams from one another for branding and reputation purposes.”


How well or poorly your contacts interact with your emails. This can be measured by looking at things like opens and clicks. Usage example: “Good engagement usually translates to good deliverability, since our reputation plays such a strong role in deliverability.”



To control the amount of email messages sent to any one mailbox provider at one time. Usage example: “This provider throttles messages when there’s large email volume originating from one sender because they may be concerned about potential spam.”

Transactional email (noun). A message sent in response to an action a user takes on a website or app. These emails contain content specific to that user, and are typically sent at the user’s request. Usage example: “Transactional emails can include password resets, shipping confirmations, purchase receipts, and payment invoices.”



To opt out of receiving further email communication from a specific sender. Users may cancel their subscription to the list or service in a number of ways, but in some countries and territories, the law requires that all emails sent to mailing lists include an unsubscribe button or similar functionality. Usage example: “I’m going to unsubscribe because this isn’t relevant to me anymore.”


A Uniform Resource Identifier (URI) is an identification string that serves as a universal identifier for a resource on the Internet. This identifier is used to access and reference a resource on the Internet. The most common type of URI is a URL, or Uniform Resource Locator. Usage example: “A URI can be used to identify any resource on the internet, such as web addresses, email addresses or files.”


The address for a website. URLs are used to locate and access websites on the web. They are composed of several different parts, including a protocol, domain name, path, and query string. The protocol is what defines how the resource will be accessed (such as HTTP or HTTPS). The domain name is the address where the website is located. The path defines the location of the resource within the domain. And the query string is used to pass additional parameters to the server. Together, these parts form a complete URL that can be used to access a website on the internet. Usage example: “Type that URL in and you’ll get to the webpage you want.”

UTM TAG (noun)

UTM stands for urchin tracking module, and is offered by Google for use with Google Analytics. UTM parameters are small pieces of URL text used to track traffic from different sources, such as social media or email, in order to help identify the origins of visits. Usage example: “This UTM tag tells me that 20% of our site visitors are coming from email.”