This document lists and explains some of the terms we use at Emarsys when dealing with customers, technical issues, etc. Please take a moment to read it; if a concept remains unclear, do not hesitate to ask. Understanding the terms below is an important step towards productivity and success.

  • Above the Fold
    The section of an email which is visible upon opening the message without any need for scrolling, considered to be the most valuable as it is what the reader sees first. Unlike a written letter the fold location varies depending on the device used to view the content (smartphone, laptop, desktop, etc.) as well as any headers placed there (e.g. webmail).
  • Authentication
    Verification of the digital identity of a sender, which in email marketing is currently categorized as one of the following: Domain Keys, DKIM, Sender ID and Sender Policy Framework (SPF).
  • Bacn
    Email that has been subscribed to but is not read until sometime after receipt, and has been called "email you want but not right now." The name is meant to imply that this mail is better than spam as the recipient has signed up to it (it comes from ‘bacon’, regarded as a superior pork product to the original Spam).
  • Blacklist
    A list of addresses, either IP or email that have been reported and listed as known sources of spam. There are two types of blacklist:

    • Private: these are built up individually
    • Public: these are published and available to everyone, sometimes for a fee.
  • Block
    Non-delivery message caused by an ISP or mail server refusing to accept delivery of an email, usually the block is categorized to indicate what may have caused it (spam or content violating policy/spam filter heuristics).
  • Bounce
    Is a non-delivery status message for mail that has been rejected. This can include block, soft bounce or hard bounce.
  • Bulk Mail
    Email sent in large volumes with generic content, mostly marketing messages, newsletters, offers, etc.
  • CAN-SPAM Act
    Acronym for the US law made in 2003 regulating commercial email sending (Controlling the Assault of Non-Solicited Pornography and Marketing Act).
  • Click-Through Rate
    Number of unique link clicks within an email compared with the total recipients of the campaign, usually expressed as a percentage. This rate is used to measure the direct response of the users to the email content.
  • Click-to-Open Rate
    Number of unique click-throughs within an email compared with the number of times the email was opened in the campaign, usually expressed as a percentage.
  • Complaint Rate
    Number of unique complaints relating to an email campaign compared with the total number of delivered messages of that campaign, usually expressed as a percentage.
  • Content Filters
    Software used to filter what content is legitimate based on text, or header information within the email itself, mostly to identify and block spam. Using content filters alone to decide if an email should be blocked or categorized as spam could lead to false positives.
  • Deliverability
    Ensuring email is delivered to the inbox as opposed to being blocked or ending up in the spam folder.
  • Delivered
    Number of emails successfully reaching the subscribers inbox, usually defined as the total volume of mail sent less any bounced content.
  • Domain
    The web address of an organization, usually its registered name, e.g.
  • Domain Name System (DNS)
    The Domain Name System (DNS) is a naming system for computers, services, or any resource connected to the Internet or network. It associates various information with domain names assigned to each of the participating entities. A DNS resolves queries for these names into IP addresses for the purpose of locating computer services and devices worldwide.
  • Domain Keys
    An authentication system that verifies that the DNS domain of a sender is correct, and confirms the integrity of the message.
  • DKIM
    DKIM stands for DomainKeys Identified Mail, which is a method of associating a domain with an email message allowing the domain owner to take responsibility for a message whilst in transit. DKIM uses the reputation of the domain to verify the message which is used in assessing if the message should be delivered or not. DKIM also allows the domain name associated with a message to be validated through encrypted authentication.
  • Double opt-in
    Where a registration is confirmed in a two-step process, meaning the user registers and then receives an email with a link that they must click to confirm that they want the content. This is to ensure that no person is subscribed by mistake (either malice or error) and acts as a safeguard for senders. See also Opt-in.
  • Email Change of Address (ECOA)
    A service that tracks email address changes and updates.
  • Email Client
    An end user program that can display and send email messages, includes software like Outlook or Mail as well as web clients such as Gmail, Microsoft Outlook (Hotmail) and Yahoo. Email clients are often referred to as Mail User Agents (MUA) as well.
  • Email Service Provider (ESP)
    A company which sends bulk mail on behalf of their clients, also known as email broadcast service provider.
  • Feedback Loop (FBL)
    A feedback method enabling complaints to be passed back to senders, typically where the end users have used the "report as spam" option.
  • From Line
    Indicates who an email is from, and is usually a combination of their address and name.
  • Greylisting
    The temporary rejection of email from a sender that is not recognized as being legitimate, but which is later accepted when it is resent. If an email is legitimate then the originating server will attempt to redeliver, and so any one-off spam attempts are dealt with. This method is not always successful, and is a controversial method for dealing with spam.
  • Hard Bounce
    Message sent to an invalid, closed, or non-existent email account, which usually gets rejected with a 500 series SMTP delivery error.
  • HTML Message
    Email message which uses HTML code to add more dynamic content such as formatting, colour, etc. but is reliant on the receiving email clients being able to render the code correctly. If the client cannot render in HTML the message will be displayed as plain text.
  • Inactives
    Term used to refer to non-responsive recipients who have not acted on any mail that they have been sent over a period of time.
  • Inbox Placement Rate (IPR)
    Number of emails delivered to the inbox compared with the number of times it was delivered to the spam folder, typically expressed as a percentage.
  • Infrastructure
    The underlying hardware that enables an ESP to send the mail on your behalf, commonly referred to as Mailing Transport Agent (MTA).
  • Invitation mail
    Messages triggered by an already subscribed user entering other peoples email addresses, usually happens with competitions or recruitment efforts. Legally this can be problematic, since the recipients have not opted-in.
  • Internet Service Provider (ISP)
    The name for an organization that provides access to the internet.
  • IP Address
    A unique numeric identifier assigned to a networked device, either static (does not change) or dynamic (changes periodically), that acts as a point of reference for the device. For email delivery a static address is preferable as dynamic addresses are more likely to trigger spam filters.
  • Junk E-mail Reporting Partner Program (JMRPP)
    The name for Microsoft’s ® feedback loop program.
  • List Fatigue
    The designation for when a list has had too many mailings sent in too short a timeframe which results in diminishing returns until the point where it becomes unusable.
  • List Hygiene
    Maintaining a mailing list by eliminating hard bounces, unsubscribes, complaints (feedback loop) and possibly inactive users as efficiently as possible so that the list membership is only populated by receptive entries.
  • List Purchase – See Bought list
  • List Rental
    The act of an advertiser (or publisher) paying a list owner to send content to their recipients without being able to access the mailing list, usually done by the list owner themselves to prevent access to the list itself. This can be successful if targeted correctly.
  • List-Unsubscribe
    Text that is included in emails (usually in the header) that enables the recipients to see an unsubscribe button that they can use to stop receiving future content. Currently this is used by Gmail, Windows Live and Cloudmark.
  • Mail Exchanger
    The device which acts as a receiving mail server, the designation for which comes from the Domain Name System (DNS). See also: MX-record.
  • MX-record
    A DNS entry which defines what kind of resource the device is and how e-mail should be routed using the Simple Mail Transfer Protocol (SMTP). For example: The MX-record for Gmail is "".
  • MTA (Mail Transfer Agent)
    A server side application that relays email messages, or delivers them to local recipients.
  • MUA (Mail User Agent)
    An end user program that can display and send email messages. See also Email Client.
  • Non-Responders – See Inactives.
  • Open Rate
    Number of recipients who opened an email compared with the total number of emails sent, usually expressed as a percentage. This rate is used as a key metric for defining an email campaign’s success, even though it uses emails sent rather than emails delivered. Text-only recipients cannot be factored in as metrics require image downloads, and users who preview the content without opening it are often erroneously counted as opens.
  • Opt-in
    Definition of a recipient’s registration status, by agreeing to have content sent to them they have Opted In. If they opt out, their opt-in status is then set to "FALSE". See also: Double opt-in.
  • Opt-out
    Opt-out is used to describe when a recipient chooses to no longer receive any content from a sender.
  • Phishing
    When email is made to look legitimate and prompts you to enter personal details or login credentials, which are then used by a scammer to masquerade as you (e.g. bank details, etc.).
  • POP (Post Office Protocol)
    An email protocol that defines how the email client accesses and retrieves content from the POP mail server, and then moves the mail to the local computer/device.
  • Postmaster
    Title of the person managing the mail servers at an organization who usually acts as a point of contact for help, further information, or to log complaints.
  • Preview Pane
    A window that email clients can offer to allow users to see some of the content of an email without having to click on the message or open it.
  • Pristine Spam Traps
    Brand new email addresses created with the sole purpose to identify spammers, which are sometimes referred to as honey pots. Emails sent to such an address will usually result in the sender, domain or IP address being blacklisted.
  • Read Rate
    Number of recipients who have marked emails as read in their mail client, usually more reliable than the open rate as it is not restricted by image downloads, expressed as a percentage.
  • Receiver
    Generic description of anyone that accepts and delivers large amounts of email such as an ISP or network.
  • Recycled Spam Traps
    Abandoned email addresses which return “unknown user” errors for between 6 and 12 months can be recycled and used as spam traps by the ISPs. Once the address is recycled it can receive mail from all senders again, which is dangerous since the mail is deliverable again.
  • Re-engagement Campaign
    Campaign designed specifically to win back inactive or non-responsive recipients.
  • Reply-to Address
    The address which receives mail when users click “reply” in their mail client, and is not necessarily the same as the originating from address.
  • Reputation
    IPs and Domains build up sending reputations based on their practices and the reactions of the recipients. This reputation is a factor that ISPs use to define if the mail should be delivered to the inbox or spam folder and to limit the amount of emails that can be delivered in a set timeframe.
  • Responsive Design
    Responsive email design is where additional code is embedded in the email, enabling it to display content based on the screen size of the device opening it. Content can be hidden or displayed as required, layout elements changed, and even different design elements can be used for different devices.
  • Return path
    "Mail from" address in the SMTP command to which bounces are returned. It defines the actual sender behind the sender address.
  • Reverse DNS (rDNS)
    The record in which an IP address is matched correctly to a domain name.
  • Sender address
    "Header from" address in the SMTP command which the recipient sees as the sender of the email.
  • Sender ID
    An anti-spam mechanism which uses a combination of Sender Policy Framework (SPF) and CallerID to authenticate senders, block forged email.
  • Sender
    This is a generic term that refers to anyone sending email, which includes companies sending to a large number of subscribers.
  • SMTP
    Stands for Simple Mail Transfer Protocol and is a standard for email transmission across IPs.
  • Smart Network Data Services (SNDS)
    A Microsoft initiative to fight spam and malware by providing data to senders based on mail sent to Outlook subscribers, including complaint metrics, SmartScreen filter results and spam trap hits.
  • Soft Bounce
    A non-delivery message indicating a potentially temporary delivery problem, which could be due to a DNS issue, a network problem, a non-reachable server or a mailbox being over the quota. Soft bounces are usually rejected with a 400 series SMTP delivery error.
  • Spam
    Spam is unsolicited mail that the recipient has not subscribed to or requested, usually sent by bot-nets to illegally acquired email addresses. Can be either:

    • Unsolicited bulk email (UBE)
    • Unsolicited commercial email (UCE)
  • Spam Filter
    A mechanism that identifies and separates spam email from legitimate email and keeps it out of the recipients inbox, usually moving it to the spam or junk folder.
  • SpamCop
    A database of blacklisted email addresses and IP addresses which is used to determine if an address has been blacklisted due to spam complaints. Formerly privately owned, but now part of the email vendor Ironport, SpamCop is a service open to everyone.
  • Spam Filter
    A mechanism that identifies and separates spam email from legitimate email and keeps it out of the recipient’s inbox, usually moving it to the spam or junk folder.
  • Sender Policy Framework (SPF)
    A protocol used to verify the authenticity of an email, which enables receiving mail servers to verify the sender before allowing the message through.
  • Spoofing
    Pretending to send mail as someone else, usually by changing the sender’s name (and sometimes address) so that it looks like the message was sent by them.
  • Sender Reputation Data (SRD)
    Used by Microsoft Live Outlook and MSN Outlook, SRD is a collection of non-biased responses from feedback loop participants over time. Along with other sources of reputation data such as the Junk e-Mail Reporting Partner Program (JMRPP), the Windows Live Sender Reputation Data helps to train and improve the way Microsoft’s SmartScreen technology properly classifies messages based on email content and sender reputation.
  • Subscribe
    The act of requesting content to be sent to you, either by email, web form or offline using a paper based form, usually so a recipient can receive a newsletter, offers, etc.
  • Subscriber
    A person who has specifically requested to join a mailing list and have content sent to them.
  • Suppression List
    All addresses that you have removed from mailing lists need to be compiled and kept to ensure compliance with the CAN-SPAM Act, which includes Opt-out or notifications via Feedback Loop (FBL). Some countries have specific Blacklists which need to be included as well (e.g. RTR/ECG Austrian suppression list).
  • ‘This is Spam’ Rate
    Number of emails flagged as junk/spam compared with the total number of emails delivered, usually expressed as a percentage.
  • ‘This is Not Spam’ Rate
    Number of emails retrieved from the junk/spam folder by the recipients compared with the total number of emails delivered, usually expressed as a percentage.
  • Throttling
    To restrict the volume of email messages that are sent to an ISP or mail server at a given time, in order to mitigate capacity issues or to prevent bounces from being generated. A good reputation will help improve the throttling rate.
  • Transactional Mail
    Transactional messages are messages that relate to purchases or orders, such as confirmation messages. The CAN-SPAM Act defines these as "facilitating, completing or confirming previously agreed upon transactions."
  • txt-record
    A DNS entry for information or authentication purposes. See also: Domain Name System (DNS).
  • Unknown User
    Bounce error code generated by an ISP when an email address does not exist. See also: Hard Bounce.
  • Whitelist
    List of approved mail senders who are never blocked or bounced. This is used by ISPs or organisations to bypass parts of their spam identification mechanisms.
  • X-header
    A user defined header element that is inserted in the HTTP header to perform a variety of actions, usually used for custom information such as enabling additional tracking, etc.