Glossary
The words, explained.
Plain-English definitions of email, IP and phone terms.
- What is a disposable email address?A disposable email address is a temporary inbox anyone can use without an account, usually deleted within minutes or hours. Here's how they work and why signup forms block them.→
- What is a catch-all email domain?A catch-all domain accepts email for any address, real or not, so you can't tell from the mail server whether a specific mailbox exists.→
- What is a role-based email address?A role account is an email address for a function or team, like info@, support@ or sales@, rather than for one person.→
- What is an MX record?An MX (mail exchanger) record is the DNS entry that says which server receives email for a domain. No MX record usually means no email can arrive.→
- What is a null MX record?A null MX record (RFC 7505) is a single MX entry pointing to '.', which tells senders the domain never accepts email.→
- What is SPF (Sender Policy Framework)?SPF is a DNS record listing the servers allowed to send email for a domain. Real businesses almost always publish one.→
- What is DMARC?DMARC is a DNS policy that tells receivers what to do with email that fails SPF or DKIM checks for a domain.→
- What is an ASN (autonomous system number)?An ASN identifies a network on the internet, such as a broadband provider or a cloud. Knowing an IP's ASN tells you who owns the connection.→
- What is a datacenter IP address?A datacenter IP belongs to a cloud or hosting provider rather than a home or mobile network. Signups from them are often automated or behind a VPN.→
- What is a Tor exit node?A Tor exit node is the last relay in the Tor network, the IP address websites see for Tor users. The list of exit nodes is public.→
- What is a VoIP phone number?A VoIP number is a phone number delivered over the internet rather than a mobile or landline network. They're cheap to create in bulk.→
- What is E.164 phone number format?E.164 is the international standard phone format: a plus sign, the country code and the number, with no spaces, e.g. +14155552671.→
- What is plus addressing (email +tags)?Plus addressing lets jane+anything@example.com reach jane@example.com. It's handy for filtering, and for creating unlimited sign-up aliases.→
- What is RDAP (and how is it different from WHOIS)?RDAP is the modern, structured replacement for WHOIS. It returns domain registration data, like the creation date and registrar, as JSON.→