IP address
An IP address (Internet Protocol address) is a unique numerical label assigned to every device connected to a network, used to identify the device and route communications to and from it. There are two current versions: IPv4, which uses a format of four numbers separated by dots such as 192.168.1.1, and IPv6, which uses a longer hexadecimal format to provide a vastly larger address space. Every device that accesses the internet, from laptops and smartphones to web servers and email servers, has at least one IP address.
In email marketing, the IP address of the sending mail server is one of the primary identity signals that receiving mail servers and spam filters use to evaluate incoming messages. Your sending IP accumulates a reputation over time based on the behaviour of emails sent from it: the complaint rates, bounce rates, and engagement levels of those sends. A shared IP carries the collective reputation of all senders using it; a dedicated IP’s reputation is entirely the result of your own sending activity and history.
For B2B email marketers, understanding the role of IP addresses in deliverability comes down to two key points. First, the IP reputation of your sending infrastructure affects whether your emails reach the inbox. Second, the IP address of email openers and clickers in your analytics can help identify non-human interactions: security scanners and bots often operate from known IP ranges, and filtering these out produces significantly more accurate engagement data for your programme.
What is the difference between a dedicated and shared IP address for email sending?
A dedicated IP address is used exclusively by one sender. All the sending behaviour from that IP is attributed to you alone, so you have full control over your IP reputation. A shared IP is used by multiple senders, typically customers of the same email service provider. The reputation of a shared IP is influenced by the collective sending behaviour of all its users. Dedicated IPs are preferred by high-volume senders who want full reputation control; shared IPs are adequate for lower-volume senders who benefit from the established reputation of the shared pool.
What is IP warming?
IP warming is the process of gradually increasing the volume of emails sent from a new or previously inactive IP address over a period of weeks. Inbox providers are suspicious of new IPs that suddenly send large volumes of email because this is a common pattern among spammers. By starting with small volumes and increasing gradually while maintaining good engagement metrics, you establish a positive sending history for the IP before scaling to full volume. Most email service providers publish recommended IP warming schedules.
Can changing your sending IP improve deliverability?
Switching to a new IP can help if your current IP has accumulated a poor reputation through previous poor sending practices. However, a new IP with no sending history starts from zero and must be warmed up gradually. The underlying causes of the deliverability problem, such as poor list quality or high complaint rates, must be addressed before or alongside any IP change. Otherwise the new IP will quickly develop the same problems. IP changes are a deliverability reset, not a fix.