Deliverability terms, defined
The records and signals InboxPlease checks, in plain language.
- SPFSender Policy Framework
- A DNS record listing the servers allowed to send email for your domain. Receivers reject or flag mail from servers not on the list.
- DKIMDomainKeys Identified Mail
- A cryptographic signature added to each email. It proves the message came from your domain and wasn't altered in transit.
- DMARCDomain-based Message Authentication
- A policy that tells receivers what to do when SPF or DKIM fail — none, quarantine or reject — and where to send reports.
- DMARC aggregate reportRUA
- A daily XML summary from mailbox providers showing which sources sent mail as your domain and whether it passed authentication.
- AlignmentSPF / DKIM alignment
- Whether the domain that passed SPF or DKIM matches the domain in the visible From address. DMARC requires at least one aligned pass.
- MX recordMail Exchanger
- The DNS record that tells the internet which servers receive email for your domain. Missing or broken MX hurts trust.
- Reverse DNSPTR record
- Maps a sending IP back to a hostname. Providers distrust IPs without matching reverse DNS.
- Inbox placement
- The share of your emails that land in the primary inbox rather than spam or promotions, measured per mailbox provider.
- Seed testPlacement test
- Sending an email to a list of monitored mailboxes at each provider to measure where it lands.
- Email warmup
- Gradually increasing sending volume and positive engagement so providers learn to trust a new or recovering domain.
- BlacklistDNSBL / blocklist
- A list of domains and IPs flagged for spam or abuse. Providers consult them when deciding where your email goes.
- Sender reputation
- The score providers assign to your domain and IPs based on authentication, complaints, bounces and engagement.
- Spam trap
- An address that never signs up for email. Mailing one signals poor list hygiene and damages reputation.
- BounceHard / soft
- A message returned as undeliverable. Hard bounces (invalid address) hurt reputation more than soft (temporary) ones.
- MCPModel Context Protocol
- An open protocol that lets AI agents call external tools. InboxPlease exposes deliverability tools over MCP.
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