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Glossary of E-mail Terminology

Community Manager
Community Manager



JSON API is a specification for how a client should request that resources be fetched or modified, and how a server should respond to those requests.

JSON API is designed to minimize both the number of requests and the amount of data transmitted between clients and servers. This efficiency is achieved without compromising readability, flexibility, or discoverability.

MX Record

An MX record is a publicly available address for an email recipients mail server

Email Service Provider

An e-mail service provider (ESP) is a company that offers email marketing or bulk email services. Sinch uses the ESP infrastructure to support the processes and governance around typical email marketing campaigns.

Domain Key Identified Mail

Technically DKIM provides a method for validating a domain name identity that is associated with a message through cryptographic (public –private keys) authentication. Identification of an emails association with a trusted domain enhances deliverability.

Sender Policy Framework

Sender Policy Framework (SPF) is a simple e-mail-validation system designed to detect e-mail spoofing by providing a  mechanism to allow receiving mail exchangers to check that incoming mail from a domain comes from a host authorized  by that domain's administrators. This also enhances deliverability.

Soft Bounce

A bounce message, also called a Non-Delivery Report/Receipt (NDR), a (failed) Delivery Status Notification (DSN) message, a Non-Delivery Notification (NDN) or simply a bounce, is an automated electronic mail message from a mail  system informing the sender of another message about a delivery problem.

A soft bounce means that the email address was valid and the email message reached the recipient’s mail server. However, it bounced back because, for example:

  • The mailbox was full (the user is over their quota)
  • The server was down
  • The message was too large for the recipient’s inbox

Hard Bounce

A hard bounce occurs when the message has been permanently rejected either because:

  • The e-mail address is invalid
  • The e-mail addresses does not exist

Open Rate

The e-mail open rate is a measure primarily used by marketers as an indication of how many people "view" or "open" the commercial electronic mail they send out.

It is most commonly expressed as a percentage and calculated by dividing the number of email messages opened by the total number of email messages sent (excluding those that bounced).

Click-through rate

Click-through rate (CTR) is the ratio of users who click on a specific link to the number of total users who view a page, e-mail, or advertisement.

It is commonly used to measure the success of an online advertising campaign for a particular website as well as the effectiveness of email campaigns.

Sender Address

This is typically a generic email address (such as, from where the marketing or transactional e-mail is being sent.

Reply to Address

When an e-mail request is received: it will typically have two values as below:

  • Sender ID: For example,; where is the registered sender subdomain
  •  “Reply To” address: For example, This is a valid e-mail address where a recipient’s reply is delivered (if needed).

The “reply to” address allows a recipient to respond back to a transactional or marketing email. When a “reply to” e-mail is sent out, the mail transfer agent looks up DNS entries to determine the MX record of the recipients mail server. The replies are sent to the Easylink Mail server from where they are forwarded to the intended recipient.

Custom “From” tag

A customer “From” tag allows a unique name to be tagged to a “sender address”. For example, if we set up the “from” tag as Mark Jones, the sender address will then show as Mark Jones <>


The Data Protection Act 1998 (DPA) helps to protect privacy rights by creating a set of rules for those who handle personal  data and by giving individuals a number of rights over their personal data and the way it is handled

Any organisation that stores and uses personal data relating to identifiable living individuals, either on a computer or in a paper filing system, is a "data controller" for the purposes of the DPA. Data controllers are obliged to handle personal data in accordance with the eight data-protection principles set out in schedule 1 to the DPA unless a specific exemption applies. The first principle is that data must be processed fairly and lawfully, which requires any processing (including disclosure) to be done either with the consent of the individual or in order to fulfil legal obligations such as contractual obligations.

Sender Score

Sender Score is a number between 0 and 100 that identifies your sender reputation and shows you how mailbox providers view your IP address. Your Sender Score is like a bank running your credit score to gauge your credit history.

Sender reputation is an indication of the trustworthiness of an email sender’s IP address. Mailbox providers take a lot of metrics into consideration to determine your sender reputation including spam complaints, mailing to unknown users, industry blacklists, and more.


Shahzad Ismail
Head of Knowledge Management and Community Engagement, Sinch