Glossary
IP address
The number that identifies a machine on the internet, which is how mail servers are known to each other.
ValidReach Team · Updated 2026-10-26
In practice
IPv4 addresses look like 192.0.2.1 and IPv6 ones are longer. A sending server has an IP address, and receivers look up its reverse DNS name and its reputation.
Verification and sending
Not a recipient matter; it identifies the server that sends your mail.