Back to main menu



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

SMS message

Short Message Service (SMS) facilitates sending text messages of up to 160 characters. In email marketing, SMS messages are sent to interested users on their mobile devices. These messages include notifications like follow-up texts, promotional coupons, or order confirmations.

SMS messaging

SMS, which stands for Short Message Service, involves sending targeted, triggered text messages to audiences offering promotions, incentives, or reminders to complete their purchase. SMS messaging usually relies on text, with the occasional use of images or emoji.

SMTP authentication

SMTP authentication, also known as SMTP AUTH, is an extension of the Simple Mail Transfer Protocol (SMTP) that adds a layer of security to email sending. SMTP is used alongside email APIs to send emails. SMTP authentication works by requiring the email sender to log in using a supported authentication method. Then, the mail server sends the email message after the sender has successfully logged in.

SMTP relay

Simple Mail Transfer Protocol (SMTP) relay, also called email relay, is the process of relaying messages from one server to the other using the SMPT protocol. SMTP relay helps to ensure that email messages are delivered quickly and reliably, even if the sender and recipient are using different email systems.

SMTP server

A Simple Mail Transfer Protocol (SMTP) server is an outgoing mail server that relays email messages brands send using the SMTP protocol. Typically, brands use two ways to send emails: SMTP or email Application Programming Interface (API). When emails are sent via SMTP, the email client relays the email via an SMTP port to an SMTP server, which authenticates the message before sending it to a receiving mail server. Lastly, the recipient’s email client retrieves the message using the Internet Message Access Protocol (IMAP).

SPF (Sender Policy Framework)

SPF, or Sender Policy Framework, is an authentication protocol that validates a sender’s identity to inbox service providers (ISPs). SPF records detail all the authorized mail servers that can send emails from a particular domain. SPF authentication provides rules to ISPs so they can recognize whether or not an incoming email message is being sent from an authorized sender. ISPs use these rules to accept, reject, or flag all incoming messages.

SSL Certificate

A Secure Sockets Layer (SSL) certificate is an encryption standard that ensures communication between two parties stays safe and secure. Websites secure with SSL certification contain an “s” after “HTTP,” like Like web pages, brands can secure email communication through SSL certification or other encryption standards like Transport Layer Security (TLS) or end-to-end encryption.

Seed test

A seed test is the process of sending emails to a select group of email addresses to troubleshoot potential email problems and gauge inbox placement rates before actually rolling out an email campaign. These tests provide brands with insights into how many emails reach  the inbox, spam folder, or no folder at all. Brands can then catch problems before they happen and determine if authentication protocols and sending infrastructure are set up to handle the email-sending traffic.

Send Time Optimization

Send Time Optimization (STO) is a feature that allows brands to send emails at the optimal time to reach every recipient. This boosts engagement rates as email messages are sent to recipients at times they’re most likely to interact with the email.

Sender ID

A sender ID is an alphanumeric code unique to each email sender. It acts as an authentication record to validate brand identities to inbox service providers (ISPs) and mail servers to prevent emails from being misinterpreted as spam.

Single opt-in

Single opt-in is the process of allowing users to subscribe to email programs in one step. It typically appears as a popup box as soon as a user visits a website, asking the user to subscribe to the brand’s communication only by sharing their email address.

Smart Network Data Services (SNDS)

Smart Network Data Services (SNDS), by Microsoft Outlook, is a free tool that provides insights into how Microsoft Outlook views the health of a brand’s IP address. SNDS also provides information about a brand’s bounce percentage, spam trap hits, and the number of emails sent from the brand’s IP address – all of which help the brand assess its sender reputation and email deliverability. Good sender reputation enables inbox service providers (ISPs) to validate the brand’s domain name and place emails in recipients’ inboxes without speculation.

Soft bounce

A soft bounce is a temporary email delivery failure that occurs for various reasons like a server outage, oversize file or message, or the recipient’s inbox hitting the storage limit. Soft bounces are usually outside the sender’s control. Most soft bounces resolve on their own after a short time. However, if they can’t be resolved, they become re-classified as a permanent delivery failure. In other words, they become a hard bounce.


Spam is unwelcomed email content that is potentially malicious or may open backdoors for hackers to lift sensitive personal details.


Spamming is the act of sending unsolicited messages or malicious content to recipients in bulk. This results in brands ending up on an email blocklist or in the spam folder, harming their IP reputation and inboxing rates. To combat this, brands can set up authentication protocols like SPF, BIMI, and DMARC, validating their domain names and protecting against bad actors.