An Internet Protocol (IP) address is a numerical identifier assigned to a device or server on a network. It allows networked systems to identify the source and destination of communication and route data to the appropriate device.
For email, the IP address identifies the mail server that sends a message. When the message reaches the recipient's email provider, the sending IP identifies the server responsible for delivering the message.
Types of IP Addresses
IP addresses are available in two main versions: IPv4 and IPv6.
IPv4 uses a 32-bit address written as four numbers separated by periods, such as
192.0.2.1. It provides about 4.3 billion unique addresses.
IPv6 uses a 128-bit address written as groups of hexadecimal characters separated by colons,
such as 2001:db8::1. IPv6 provides a much larger address space to accommodate the growing number
of internet-connected devices.
Shared vs. Dedicated IP Addresses
Email services can use either a shared IP address or a dedicated IP address.
A shared IP address is used by multiple senders. Sending activity from those senders contributes to the IP's overall reputation.
A dedicated IP address is assigned to one sender or organization. The sending activity associated with the IP is therefore tied to that sender, making the IP reputation easier to monitor separately.
Why Is an IP Address Relevant to Email?
The sending IP is part of the technical information available to the recipient's email provider when a message arrives. The provider can evaluate the IP's sending history and reputation, along with other signals, when making delivery decisions.
An IP address can also appear on email blocklists if the associated sending activity violates the criteria used by a blocklist operator. Monitoring the sending IP can therefore help businesses identify reputation and deliverability issues.