What’s the difference between the sending IP and domain IP?

You might assume your domain has one IP address that handles everything. Makes sense, right? But your website and your email are usually running from completely different places, and that means completely different IPs.

The domain IP (A record) is where your website lives. When someone types harborpost.net into a browser, the A record points them to that IP. It's a web hosting address. It has nothing to do with your email.

The sending IP is what your mail server uses when it connects to a receiving mail server to deliver an email. That IP could belong to your ESP, a dedicated mail server, or a shared sending pool. It's almost never the same as your website's IP.

Why do they differ? Because web hosting and email sending are separate jobs. If you use Mailchimp or Postmark to send your emails, they're sending from their own IPs, not yours. Your website might be hosted on a totally different server in a totally different data center. That's completely normal.

Where this actually matters is SPF authentication. SPF is a list of IPs that are allowed to send email on behalf of your domain. It cares about the sending IP, not your domain's A record. If you publish your website's IP in your SPF record instead of your ESP's sending IPs, your emails will fail authentication. (That's a more common mistake than you'd think.)

PTR records (reverse DNS) also apply to the sending IP, not the domain IP. Mailbox providers use those to check whether your sending IP resolves back to a legitimate hostname, which is part of how they judge your sender reputation.

So when you're troubleshooting authentication or deliverability, the domain IP is largely irrelevant. What matters is which IP is actually doing the sending, and whether your DNS records account for it.

Not sure your SPF is covering the right IPs? You can check in seconds with our free SPF checker.