Deliverability Terminology


Businesses depend on email, and it's important to keep up to speed on concepts about deliverability. Mailbox providers have gotten smarter and more complex when filtering emails and placing them in the inbox. Being up to date on terminology and concepts means you can shift sending strategies to focus on key concepts and achieve the best deliverability possible.

Not sure where to start? We have compiled a list of common deliverability terms below that you can familiarize yourself with and use the knowledge in your interactions with clients.

Click one of the letters below to view terms and definitions.

A   B   C   D   E   F   G   H   I   L   M   O   P   R   S   T   U   W


A Record: A type of record maps a domain name to the IP address hosting the domain.

Anti-Spam: Using software and back-end processes to block spam from entering a system or domain.

Average Open Rate: Average open rate is the percentage of email recipients that open an email message from a sender. Visit How can I improve my open rate for more information on open rates and how to improve them.

Authentication: Refers to the process of setting up DNS records for DKIM, DMARC, and SPF. These methods of email authentication solidify the reputation and security of your emails to improve deliverability and prevent phishing. Setting up Authentication is accomplished by adding a Sending Domain in ActiveCampaign.


BIMI (Brand Indicators for Message Identification): a type of DNS record that is used to display a company logo inside an email inbox.

Block: This occurs when a message is rejected by the recipient domain without first attempting to deliver it to the inbox.

Blocklist: Blocklists are used by various providers and services to track and penalize senders for sending spam. While most are low priority, there are several blocklists to watch out for, such as SpamHaus, Invaluement, Proofpoint, and Barracuda. Being on these lists can result in deliverability issues such as spam placement and mail rejection. Visit The hype and truth of email blocklists for further details about blocklists. 

Bots: Malicious emails and procedures used by hackers to flood forms with email traffic, mark emails as spam, and cause delivery issues due to non-legitimate emails being put into sender lists. Visit Why do I have spam contacts in my account for more information about bots/spam contacts. 

Bounce Rate: The percentage of messages that are not accepted for delivery by a recipient domain. A contact is labeled as bounced when an email campaign that is sent to them is rejected by their receiving email server. These rejection notices indicate the email address is either invalid or inaccessible.


CAN-SPAM Act: The Controlling the Assault of Non-Solicited Pornography And Marketing Act is a law that sets the rules for commercial email sending in the United States. Visit CAN-SPAM Act: A Complete Guide for Business for more information.

CASL: Canada's Anti-Spam Legislation, the federal law that controls and is in charge of regulating and preventing spam and other various election threads. To be compliant, one must obtain consent, provide identification information, and also an unsubscribe procedure. Visit Canada's Canada's Anti-Spam Legislation for CASL details.

CCPA: California's Consumer Privacy Act, which gives California consumers new privacy rights and control over personal data that businesses can collect from them. Included are the rights to opt out of the sale of personal information, their right to know about what information a business collects, and how it is used and shared - among others. For more information, visit this CCPA overview page.

Click to Open Rate (CTOR): A metric that measures the effectiveness of your email's content. It is calculated by the number of unique clicks divided by the number of unique opens.

Click-Through Rate (CTR): A ratio that compares how many people click a specific link to the number of total users that view a webpage or email. It's used as a metric to measure the success of a marketing campaign. To calculate your email CTR - take the number of people that have clicked on a link in your email, divide that by the number of emails delivered, and multiply that number by 100 - to get a percentage.

Clipping: This occurs when an email is sent that exceeds a file size, at which point the email mail is "clipped" and requires the user to click on a prompt to see the full message. 

CNAME: A record used to create and map an alias from one domain to another. They are typically used to map a subdomain (such as mail. for example) to the domain being hosted. CNAMEs at ActiveCampaign specifically are used so that instead of logging in at the default you can use something like or

Confirmed Opt-In (COI): Also known as Double-opt in (DOI). A process for confirming that recipients want your email. Involves recipients confirming their subscription via a form, email, clicking a link, or other means. Visit What is an opt-in list for more information on opt-ins.

Consent: A recipient opting in to receiving communications. They are giving their permission to be contacted by the sender.


Dedicated IP: A static IP address that is only used to send email on behalf of one sender/company/brand, which is responsible for the content of all the messages sent from that IP. There are specific requirements in order to be able to use a dedicated IP at ActiveCampaign.

Deferral: This occurs when messages are held up at the domain level for a period of time before being accepted and routed for delivery - or rejected.

Deliverability: Deliverability is the measurement of email success in reaching a contact's inbox. Overall email deliverability is impacted by many factors, including list quality, domain reputation, content, and identification as spam via complaints. Because there are so many factors, improving deliverability is a constant goal. Staying on top of best practices will help you achieve goals more efficiently and consistently.

Delivery: Delivery tells you whether or not your emails were received by the servers of your subscriber's inbox providers. An email counts as delivered if it did not bounce. It does not take into account other details (placement for example) - that's where deliverability comes in.

DKIM (DomainKeys Identified Mail): An authentication piece that supports transparency by identifying the sender of a message and providing a "signature" by way of a key that verifies the sender as legitimate and allows ESPs to send their behalf. 

DMARC (Domain Message Authentication Reporting & Conformance): An email authentication/policy/reporting protocol that is designed to give email domain owners the ability to protect their domain from unauthorized use. There are three policies that a domain administrator can implement (none, quarantine, reject) - and mail will be filtered or blocked based on the policy and the level of authentication. Caution should be used when implementing policies, as misconfigurations can cause deliverability issues specific to the DMARC policy when using ActiveCampaign.

DNS (Domain Name System): The Internet's system for converting alphabetic names into numeric IP addresses. For example, when a URL address is typed into a web browser, DNS servers return the IP address of the Web server associated with that name.

Domain Reputation: Domain reputation is the overall health of your branded domain as interpreted by mailbox providers. This reputation is determined by various factors such as engagement, spam complaint rates, spam traps, bounce rates, and your sending history.


Email Click Rate: Email click rate is the percentage of people who click on an email link after receiving an email campaign. Email click rates measure the immediate response rate of an email and are often used as the primary conversion metric for a campaign.

Email Harvesting: The process of obtaining lists of email addresses from various sources in order to send illegitimate bulk email campaigns.

Email Service Providers (ESPs): These are platforms designed to send different types of emails on behalf of customers. ActiveCampaign, MailChimp, and Constant Contact are some examples. Visit ActiveCampaign's Approach to Deliverability for specifics.

Engagement: The various ways in which a contact interacts with your emails - opens, clicks, and responses to name a few. Engagement is a key tenet of deliverability and is crucial to keeping sender reputation high.


Feedback Loop: A process that allows a sender to receive a report every time a recipient clicks on the "mark as spam" button. Mailbox providers deploy email feedback loops in order to reduce the spam received by their end users. The system is provided so that senders can identify and address the problems causing the complaints.


GDPR: General Data Protection Regulation, a regulation on data protection and privacy standards in the EU. It requires businesses to protect the personal data and the privacy of citizens for transactions and communications that occur between the member states of the European Union. Learn more about GDPR


Hard Bounce: A permanent error. Occurs when the address/domain doesn't exist at all. This can be caused by anything from typos to deleted user accounts. If you receive a hard bounce, immediately removing them from your list is the best course of action, as a hard bounce indicates a permanent reason that an email cant be delivered and that this address should not be mailed to in the future.

Header: Contains identifying routing information of the message, including the sender, recipient, date, and subject. Reviewing email headers and source code can help identify potential delays, issues, or reasons for mail not being delivered.

Honeypot: Inactive email addresses set up specifically to catch spammers. These emails are not used by real people and therefore never opted-in to any email campaigns. So if a sender tries to send to these addresses, they will be flagged.


Internet Service Providers (ISPs): Companies that provide access to the internet to both personal and business customers. Oftentimes, these providers also provide email inboxes to their customers as part of their service. Verizon Media and Comcast are examples of ISPs.

IP Address: A unique string of characters that identifies each computer using the Internet Protocol to communicate over a network.Used to distinguish senders, websites, etc., and allow the transfer of information between addresses.

IP Block: Blocks and listings that occur on a specific IP.

IP Reputation: Based on various metrics a mailbox provider has historically seen from that IP address and how users engage with mail that originates from it, both positively and negatively.


LGPD: General Law for Personal Data Protection, a law that is applicable to companies and individuals who use personal information belonging to Brazilians located in Brazil at the time the data is gathered. The law considers any information related to a person as personal data. Actions that can be performed with personal data - such as collecting, accessing, or distributing - must have a legal basis such as consent or legitimate interest order to be in compliance. Learn about the specifics of the LGPD.

List Hygiene: This is a process where you remove inactive, bounced, and other non-engaging email addresses from your lists on a consistent basis. Keeping subscribers on your email list who have no interest reduces your deliverability rates. ActiveCampaign can help you clean your lists using various methods and automations so you are sending the cleanest data possible from our platform.

List-Unsubscribe: Code added to all emails sent from the ActiveCampaign platform. Mailbox providers that support the functionality (such as Gmail) may display an unsubscribe button in the user interface or implement backend functionality to help manage unsubscribe requests.


Mailbox Providers: Companies who offer email inboxes for their customers and consumers. The level of sophistication in regards to filtering is more comprehensive as opposed to ISPs. Gmail and Hotmail are examples of mailbox providers. 

Mail Exchange Record (MX): This record includes the mail server responsible for accepting email messages on behalf of a domain name.

Mail Transfer Agent (MTA): Software that transfers electronic mail messages from one destination to another.

Mailserver Domain: Also known as the Return Path, Mail From, Envelop From, or Bounce Address domain. This is the domain that is checked for SPF and where bounces are returned if one occurs. This domain is different than your "From" address domain and is only visible if you inspect the message. The Mailserver Domain is set up when you add a Sending Domain.


Opt-Out: When a recipient opts out, it means they no longer wish to receive communications from a specific sender. In many cases, opting out involves clicking the unsubscribe link in an email and therefore being added to an exclusion list.


Phishing: Sending fraudulent emails under the guise of pretending to be a reputable company and sender. These emails are used to target and obtain an individual's personal information.

Postmaster: The persons or entities responsible for managing a specific domain as it relates to support requests - such as block removals and various deliverability issues.

Pristine Spam Trap: Email addresses that are specifically used by ISPs and mailbox providers to identify and reject senders who have obtained these addresses through illegitimate means.


Recycled Spam Trap: Old email addresses which are no longer in use are re-purposed to catch abusive mail and spammers.

Return Path: Also known as the Mailserver Domain. The return path is an email header that indicates where and how bounced emails will be processed. This is also the domain checked for SPF. When adding a Sending Domain you set up a Mailserver Domain to use your domain as the Return Path.


Safelist: Lists or filters that your recipients can create in their respective email clients. When a sender is added to a safe sender list, their emails are more likely to be delivered to the inbox. This also helps ensure that recipients won't miss future messages that they opted into receiving.

Segmentation: A way of separating your contact lists - it is recommended to split lists into active and inactive segments. Active refers to those who have opened or interacted with an email in the last 60-90 days. Inactive refers to recipients with little to no activity historically since sending to them.

Sender-ID: A now deprecated authentication protocol designed to protect against exploits such as phishing and domain spoofing.

Sender Policy Framework (SPF): TXT records on your domain that authorize certain specific to send email using your domain name. By setting up a Mailserver Domain, SPF will pass for all messages - but you can add our SPF records for additional domain authentication.

Sending Domain: The brand/domain a person or company has purchased for themselves or their business to use for email marketing. is an example of a sending domain.

Shared IP: An IP that has many different senders using it simultaneously.

Simple Mail Transfer Protocol (SMTP): The process used to transfer and send email over the Internet.

Single Opt-In (SOI): The process of a recipient indicating that they wish to receive the messages from a particular sender. This can be done via forms, emails, and other means.

Soft Bounce: Indicates that an email cannot be delivered to the recipient due to temporary failures such as: a full mailbox, a connection problem, a technical issue at the mailbox provider, or deferral of the connecting IP by the mailbox provider due to volume thresholds and other various factors. At ActiveCampaign, a contact can soft bounce three times before it is removed from further sends.

Spam: Bulk messages that are sent without explicit consent of the recipient.

Spam Complaints: An action taken by the end user to report your email as spam, this is done by hitting the "mark as spam" button in your respective email client. These are reported to providers and ESPs; if you have a high spam complaint rate (over 0.10%), your sender reputation can come down which can lead to deliverability issues.

Spam Placement: Emails being routed to spam folders for recipients. This can be for a various of reasons, but mostly centers around sender reputation and content.

Spam Trap: An email address that does not belong to a real person or used for any kind of communication. They are commonly used by mailbox providers and blocklist services to catch senders who have poor list hygiene or may not be sending to opted in lists. Visit Spam traps and how to prevent them for more details regarding spam traps.

Spear Phishing: An effort to target a small group or specific individual to gain information or access. Pretending to be a bank in an email sent just to a person with that bank is an example of spear phishing.

Spoofing: A tactic used by spammers in which they falsely identify themselves as a means to acquire access to a system to steal data, spread malware, and can be used through various forms such as IPs, emails, and text messages.

Subdomain: An extension of a base domain. For, marketing. is the subdomain. Subdomains are useful in terms of deliverability, as they can be used to isolate mail streams from one another for both branding and reputation purposes.

Suppression: The automated process of contacts being removed from your lists due to reasons such as an invalid email, too many soft bounces for a particular contact, or the contact has unsubscribed. Contacts who are suppressed are added to an exclusion list.


Throttling: Controlling the amount of email messages sent to a mailbox provider at one time. Sometimes providers will throttle messages when there is a large amount of volume originating from one sender because they may be concerned about potential spam.

Transactional Email: Transactional emails are messages sent in response to an action a user takes on a website or application; they contain data or content that is specific to that user and are typically sent to individuals one at a time—some examples include password reset emails, shipping confirmations, payment invoices, and purchase receipts. 

In contrast, marketing emails (also called promotional, broadcast, commercial, or bulk emails) are mass distributions of the same message to many recipients simultaneously.

You can send transactional emails from ActiveCampaign thanks to our Postmark integration.

TXT Record: A type of DNS record that contains text information for sources outside of your domain. You add these records to your domain settings. You can use TXT records for various purposes. For example, Google uses them to verify domain ownership and to ensure email security.

Typo Trap: an email address with a misspelled domain name used to catch senders who have poor list hygiene practices.


Unsubscribe: When emails are no longer relevant or important to a contact, they can unsubscribe to cancel their subscription to the list or service. In some countries, the law requires all emails sent to a mailing list to include an unsubscribe button or similar functionality. On our platform, you are able to manage your unsubscribes as well.


Verification: The process of verifying that you own your domain so that we can allow you to use it for email sending with ActiveCampaign. This is accomplished by logging into your DNS provider when adding a Sending Domain or by clicking a link in a verification email that is sent to you during the Manual process of adding a Sending Domain. You will need to verify all sending domains before you use them for campaigns or automation emails within ActiveCampaign.


Warm Up: The process of starting with smaller sending volumes and scaling up over time to help build sending history and reputation. This is particularly important when migrating to ActiveCampaign from another provider. A usual warm up will take about 30 days on average. 

Whale Phishing: Targeting a group or company to gain sensitive information by imitating a key stakeholder at the company. Pretending to be the CEO and asking to have money transferred from one business account to another is an example of whale phishing.

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