Glossary Archive

The human-visible sender name shown in an email client’s From field.

The email address in the message header’s From field (RFC 5322), which may differ from the envelope-from/return-path.

A trap address intended to catch unsolicited mailers (often synonymous with a pristine spam trap). Sending to honeypots signals poor acquisition practices.

Recipients who have not engaged (opens/clicks/replies) within a defined time window; often targeted for re-engagement or suppression.

The percentage of messages that land in the inbox (vs spam or missing), often measured via seed-list testing.

The outcome/goal of having email delivered to the recipient’s inbox rather than spam or being blocked.

A company that provides internet access (e.g., AT&T, Verizon, Comcast). In email deliverability, “ISP” is sometimes used loosely to mean a mailbox provider. In deliverability discussions, ISP is sometimes used loosely to mean mailbox providers (Gmail, Yahoo, Microsoft), though ISPs also include internet access providers (AT&T, Verizon, Comcast).

A numeric identifier for a server/device. In email, sending IPs (shared or dedicated; static or dynamic) influence reputation and deliverability.

A numeric network address. In email, sending IP reputation affects deliverability; IPs may be dedicated or shared and static or dynamic.

A delivery issue caused by poor IP reputation or IP-based blocklisting, often resulting in rejects, deferrals, or spam placement.