Email Glossary

Acceptance rate measures the percentage of emails accepted by receiving mail servers without bouncing. Unlike deliverability rate, acceptance rate includes all non-bounced emails regardless of whether they reach the inbo...

Backscatter is automated bounce messages sent to innocent third parties whose email addresses were forged by spammers. When spammers send mass emails using fake sender addresses, mail servers generate bounce notification...

A blocklist (also called a blacklist or denylist) is a real-time database of IP addresses and domains identified as sources of spam, fraud, or other malicious email activity. When your sending IP or domain appears on a b...

Email bounce rate is the percentage of sent emails that could not be delivered to recipients' inboxes. It is calculated by dividing the number of bounced emails by the total number of emails sent, then multiplying by 100...

An email complaint occurs when a recipient marks an email as spam or junk using their email client's reporting feature. The complaint rate measures the percentage of recipients who flag your emails as unwanted, typically...

DDoS (Distributed Denial of Service) is a cyberattack where multiple compromised systems flood a target server or network with overwhelming traffic, causing service disruption. In email infrastructure, DDoS attacks can c...

Email deliverability refers to the ability of your emails to successfully reach recipients' inboxes rather than being filtered to spam folders or blocked entirely. It encompasses multiple factors including sender reputat...

Domain reputation is a score that email providers assign to your sending domain based on the historical behavior of emails sent from that domain. Unlike IP reputation which can change when you switch email providers, dom...

Email bounce handling is the process of managing and responding to emails that fail to reach their intended recipients. It involves detecting bounced emails, categorizing them by type (hard or soft bounce), taking approp...

Email deliverability is the measure of how successfully your emails reach recipients' inboxes rather than being filtered to spam folders, blocked by ISPs, or bouncing back entirely. It encompasses a complex interplay of...

Email fatigue occurs when recipients become overwhelmed, disengaged, or annoyed by receiving too many emails from a sender or in general. This psychological response leads subscribers to ignore, delete, or unsubscribe fr...

Email infrastructure refers to the complete technical foundation that enables sending, receiving, routing, and managing email communications. It encompasses mail servers (SMTP, IMAP, POP3), DNS records for authentication...

Email rate limiting is a control mechanism used by email service providers and mailbox providers to restrict the number of emails that can be sent or received within a specific time period. This practice helps prevent se...

Email throttling is the practice of controlling the rate at which emails are sent to manage delivery speed and protect sender reputation. It involves limiting the number of emails sent per hour or day to avoid triggering...

Email warmup is the process of gradually increasing email sending volume from a new or dormant email address to establish a positive sender reputation. This systematic approach signals to email providers that you are a l...

A feedback loop (FBL) is a service provided by email providers that notifies senders when recipients mark their emails as spam. When a subscriber clicks the spam button in their inbox, the email provider sends a report b...

Greylisting is an anti-spam technique where mail servers temporarily reject emails from unknown senders, returning a "try again later" response. Unlike blocklisting, greylisting is a temporary measure that tests whether...

A hard bounce is a permanent email delivery failure that occurs when an email cannot be delivered due to a permanent reason, such as an invalid email address, non-existent domain, or blocked recipient. Hard bounces shoul...

Inbox placement rate (IPR) is the percentage of sent emails that successfully land in recipients' primary inbox rather than spam folders, promotions tabs, or being blocked entirely. It is a more accurate measure of email...

IP reputation is a score that email providers assign to the IP address used for sending emails. This score reflects the sending history and trustworthiness of that IP address. A good IP reputation means your emails are m...

IP warming is the gradual process of establishing a positive sending reputation for a new or dormant IP address by systematically increasing email volume over time. This practice signals to email service providers (ESPs)...

IP warmup is the strategic process of gradually increasing email sending volume from a new or dormant IP address to establish a positive sender reputation with Internet Service Providers (ISPs). This technique involves s...

List hygiene is the practice of regularly cleaning and maintaining your email list to remove invalid, inactive, and problematic email addresses. Good list hygiene improves email deliverability, reduces bounce rates, prot...

The postmaster is the administrative email account responsible for managing an email domain's mail system operations. This account receives automated notifications about bounced messages, delivery failures, and abuse rep...

A queued email is a message that has been composed and submitted for delivery but is temporarily held in a waiting state before being sent. This happens when the email server cannot immediately process the message due to...

Rate limiting is a technique used by servers and email providers to control the number of requests or actions a user can perform within a specified time period. It serves as a protective mechanism against abuse, spam, an...

Sender reputation is a score assigned by email service providers to your sending IP address and domain based on your historical email sending behavior and recipient engagement patterns. This score directly determines whe...

A shared IP address is an IP that multiple senders use to dispatch their emails through the same email service provider. This arrangement allows smaller businesses to send emails without the cost of maintaining a dedicat...

A soft bounce is a temporary email delivery failure that occurs when an email cannot be delivered due to a temporary issue, such as a full mailbox, server downtime, or message size limits. Soft bounces may succeed on ret...

Spam refers to unsolicited bulk email messages sent without recipient consent, typically for commercial, fraudulent, or malicious purposes. Also known as junk mail, spam emails are distributed en masse to large recipient...

A spammer is an individual or entity that sends unsolicited bulk emails to recipients who have not opted in to receive them. Spammers typically distribute irrelevant, deceptive, or malicious content to large numbers of e...

A suppression list is a database of email addresses that should never receive emails from your organization. It includes addresses that have bounced, unsubscribed, filed spam complaints, or been manually added due to leg...

Email throttling is the practice of limiting the rate at which emails are sent to control delivery speed and prevent overwhelming recipient servers. It can be implemented by senders to protect their reputation or enforce...

A whitelist is a list of approved email senders that recipients or email service providers have designated as trusted and safe. Emails from whitelisted senders bypass spam filters and are delivered directly to the inbox,...