Email Glossary

Bounce codes are automatic messages sent from a mail system to inform you of a delivery problem. These messages are called non-delivery reports (NDRs), or bounces. Bounce reports may be returned synchronously in the course of the Simple Mail Trans...

Cascading Style Sheets (CSS) is a simple method used to apply format and style (including typographical fonts, spacing, colors, and layout options) to a page in a markup language such as HTML. 

Connection and throughput settings refer to the number of simultaneous Simple Mail Transfer Protocol (SMTP) connections a Mail Transfer Agent (MTA) can open on a mailbox provider's receiving server, and the number of messages they can send over ea...

Inactives, also referred to as inactive subscribers or non-responders, are email recipients who have taken no action on their emails, such as opens or clicks, within a certain amount of time. 

Inline Cascading Style Sheets (CSS) uses style information placed directly into a single HTML element instead of residing in a separate CSS file.  For example: <h1 style="color:red;"> Heading</h1>    

When you use non-organic list acquisition, you add recipients to your email program without their consent.   Examples of non-organic list acquisition methods are: List purchase List rental List harvesting Email appending Import address book    

Organic list acquisition is when subscribers are added to your email program with their consent. Examples of organic list acquisition methods are: Website form Retail point-of-sale Social media    

X-headers are custom email headers added into email in addition to the standard headers, such as the To, From, and Subject, according to the specific needs of the sender. Mailbox providers also add X-headers to email for authentication results, sp...

To unsubscribe means to remove yourself from an email list, either via an email to the sender, an emailed command to the list server, or by filling in a web form.

A block is an action mailbox providers take when they refuse to accept unwanted or unsolicited email for delivery. Mailbox providers put in place spam-blocking measures to help sort through incoming email, identifying the legitimate email and the ...

A blocklist is a list of IP addresses or domains exhibiting characteristics of spam. Mailbox providers and spam-filtering companies use a blocklist to identify IP addresses and domains suspected of sending spam to aid their filtering decisions. Th...

Bogons are legitimate IP addresses that have not yet been allocated or delegated by the Internet Assigned Numbers Authority (IANA) or a delegated Regional Internet Registry (RIR). This includes: IPv4 fullbogons: Which encompasses the traditional ...

A botnet is a network of computer devices infected and controlled by an unauthorized third party using malicious software. Botnets are used to send spam from infected computer devices often without the knowledge of the device owner.

A bulletproof button is a button within an email that is built using HTML instead of an image. By using HTML code instead of an image, the button displays in email clients when images are turned off.

A call to action (CTA) is an instruction to an email recipient that encourages a specific, measurable action. For example, you would use a CTA when you want your subscriber to sign up for a newsletter or make a purchase. The CTA typically uses ph...

A Canonical Name (CNAME) record is a type of Domain Name System (DNS) record used to specify that a domain or sub-domain is an alias for another domain or sub-domain. For Example: If you have a knowledge base for your clients that can be accessed...

A captcha prompts computer users to confirm they are not computer program or bot, typically by asking them to read distorted text or an image and type it into a box. Computer programs typically have difficulty reading distorted text or images. Whe...

A complaint feedback loop (FBL) is a service offered by participating mailbox providers, in which they provide you with copies of complaints generated when your subscribers report your email as spam.  List of all available complaint feedback loop...

The complaint rate is a rate which shows how often your subscribers complain to mailbox providers about receiving your email. Mailbox providers calculate complaint rates by dividing the number of complaints by the number of messages delivered to y...

A conversion rate is the percentage of your subscribers that follow your call to action in an email marketing campaign. For example, if you send an email to your subscribers with a call to action that reads Buy now, the percentage of your subscri...

A cousin domain, which is also referred to as a look-alike domain, is a Domain Name System (DNS) domain that looks similar to another name when rendered by a Mail User Agent (MUA).For example, groupA.example is a cousin domain of group.example. Ot...

A dedicated IP address is one that is owned and operated by a single company to send email. Senders must purchase and set up the dedicated IP themselves or through an Email Service Provider (ESP).  

A dedicated server is a server that is used by only one sender. A dedicated server performs better than a shared server. Emails go out faster, the server is more secure, and you eliminate the possibility that another sender could get the server b...

A defensively registered domain is a domain that is not intended for use, but is registered so no other entities can own it. Defensively registered domains are considered strong candidates to implement Domain-based Message Authentication, Reportin...

A deferral is a temporary refusal by a mailbox provider or mail server to accept an email message for delivery.  The message is temporarily deferred but may be accepted at some point in the future.  There are several reasons your email may be defe...

A dictionary attack, also called a dictionary harvest attack, is a method used by spammers to harvest email addresses. This is usually done by using a program that guesses valid email addresses at a domain using different variations of common use...

Disposable email addresses are addresses that have no long-term value to the owner and are easily discarded. They are often used in submission and sign-up forms when the owner is: Skeptical of the trustworthiness of the website Concerned about re...

A domain blocklist (DBL) is a database of spam domains that includes: Spam URLs Sender domains known to be spammers Domain blocklists contain a domain name instead of an IP address.

Domain names are used to identify one or more IP addresses. They are used in Uniform Resource Identifiers (URIs) to identify particular webpages, and also used in email addresses. For example: domain.com someone@domain.com.

Dynamic Internet Protocol (IP) addresses are frequently changing IP addresses that are assigned by Internet service providers for residential and business customers. Dynamic IP addresses allow many devices to share limited address space on a netwo...