What is an IP address in the context of email sending?
Still have a question, spotted an error, or have a better explanation or a source we should cite?
An IP address in email is the numeric identifier (like 203.0.113.45) of the mail server that's physically sending your message. When your email leaves your ESP or mail server, mailbox providers see that IP address in the connection logs and use it to make filtering decisions.
Here's how it works in practice. When SendGrid or Mailchimp sends your email, their server connects to Gmail or Outlook's servers. The first thing those receiving servers see is the sending IP address. They check: has this IP sent spam before? Does it have a clean history? What's its complaint rate? That reputation history determines whether your email lands in the inbox or gets filtered.
There are two types of sending IPs: shared and dedicated. A shared IP is used by multiple senders at once (most small senders use shared IPs through their ESP). A dedicated IP is yours alone. Shared IPs pool reputation across all senders using them, which means your neighbor's bad practices can affect your deliverability (and vice versa). Dedicated IPs give you full control over reputation, but you need to send enough volume (usually 100,000+ emails per month) to build a stable reputation. If you send sporadically on a dedicated IP, mailbox providers see an inactive IP that suddenly bursts with mail, which looks suspicious.
Most ESPs handle IP management for you. If you're on Mailchimp, Brevo, or Klaviyo, you're using their shared IP pools by default. If you send high volume and want a dedicated IP, most ESPs offer it as an add-on. But here's the catch: switching to a dedicated IP means you start from zero reputation. You'll need to warm that IP gradually by sending to your most engaged subscribers first, then expanding volume over 4-6 weeks.
If you're troubleshooting delivery issues, check whether your sending IP is blocklisted. Our free blocklist checker scans your IP against major blocklists in seconds. If you're stuck deciding between shared and dedicated IPs for your setup, ask us and we'll walk through what makes sense for your volume.
Contributors
Who worked on this answer
Every name links to their profile. Every company links to their site. Real people, real accountability.
