Lost in all the technical jargon? Find definitions for common email and technical terms and learn more with our related resources.

MIME (Multipurpose Internet Mail Extensions)

Multipurpose Internet Mail Extension (MIME) increases the sending capabilities for non-ASCII (non-American Standard Code for Information Interchange) data files like audio, video, images, and apps within emails. MIME is an extension of the Simple Mail Transfer Protocol (SMTP).

MX record

A Mail Exchange (MX) record describes how an email should be relayed and routed to the end user. It’s also called a Domain Name System MX record, or DNS MX record, because it directs email from a domain to a server via the Simple Mail Transfer Protocol (SMTP). This ensures the email is relayed from the sender to the receiver.

Mail Transfer Agent (MTA)

A Mail Transfer Agent (MTA) is an email server software that receives and relays emails. An MTA receives messages from another MTA or from a Mail User Agent (MUA), which is a computer application that end users use to access or send emails. Once an MUA relays an email to an MTA, the MTA takes over and sends it to the receiving MTA via Simple Mail Transfer Protocol (SMTP). If the sender seems spammy, inbox service providers (ISPs) will restrict the email delivery, potentially impacting the brand’s deliverability.

Mail user agent (MUA)

A mail user agent (MUA), also called an email client, is a mail client application that grants users access to a mail server in order to create, send, and receive email messages. MUA examples include Microsoft Outlook, Gmail, and Apple Mail.

Marketing automation

Marketing automation refers to the process of automating steps in a brand’s communication strategies. In email programs, marketing automation boosts efficiency and improves ROI by integrating with Customer Relationship Management (CRM) software, mechanizing lead nurturing, and allowing senders to trigger automations based on recipients’ engagement with the emails.

Message ID

A message ID is the unique identifier issued by an email service provider (ESP) used to track a specific message. This ID is composed of a string of random alphanumeric characters, and it’s unique to the message sent to recipients, regardless of how many recipients there are. It also includes the email client’s name to indicate the sender. Here’s an example: