Glossary Archive

A delivery outcome where an email does not reach the recipient due to issues such as bounces, blocks, or repeated deferrals/timeouts.

A complaint-reporting program where mailbox providers send spam-complaint signals to senders so they can suppress complainers and reduce future complaints.

A program where mailbox providers report user spam complaints back to senders so they can suppress complainers and reduce abuse.

Fully Qualified Domain Name: the complete hostname including all labels and the domain (e.g., mail.example.com).

General Data Protection Regulation: EU privacy law governing personal data processing, consent, and data-subject rights, with global reach for EU residents’ data.

EU data protection regulation governing how personal data is collected, processed, stored, and used, including consent and data-subject rights.

Gmail’s reporting tools that provide visibility into domain/IP reputation, spam rate, and delivery issues for authenticated senders.

A receiving-server technique that temporarily rejects mail from unknown senders (usually with a 4xx code). Legitimate senders retry; spammers often do not.

A permanent delivery failure to an invalid/closed/nonexistent mailbox, often indicated by 5xx SMTP codes. Hard-bounced addresses should be suppressed.

Email metadata containing routing and authentication results (SPF/DKIM/DMARC), timestamps, and other diagnostics added by servers handling the message.