What is IP reputation today vs 10 years ago?

Ten years ago, IP reputation was the whole game. Mailbox providers looked at which server sent the message and judged the sender based on that IP address's history. A good IP meant good delivery. A tainted IP meant spam folder, or worse, a block. Dedicated IP addresses were considered essential for any serious email program, and warming a new IP was step one of every deliverability playbook.

The problem? Spammers figured this out fast. When an IP got burned, they'd simply abandon it and spin up a fresh one. Mailbox providers had to adapt.

So they shifted focus toward domain reputation. Instead of asking "which server sent this?", filters started asking "which domain is behind this?" You can change your IP overnight, but your sending domain is tied to your brand, your history, and your authentication records. It's a much harder signal to fake.

Today, at Gmail, domain reputation is the dominant signal. Gmail processes roughly 30% of global email, so this shift matters enormously for most senders. Your domain's track record, your engagement history, your complaint rates, and your authentication setup carry far more weight than the server address your message came from.

That said, IP reputation hasn't disappeared. Microsoft 365 and enterprise-grade spam filters still lean heavily on IP-based signals and blocklists. If your IP lands on a major list, you'll feel it in deliverability at Outlook and corporate inboxes even if your domain is in great shape. Both signals co-exist. Domain just leads now at the providers with the most reach.

What this means practically:

• Small or mid-size senders on a shared IP pool at a reputable ESP don't need to panic about IP reputation. Focus on your domain and your list hygiene instead.
• High-volume senders (generally above 200,000 to 500,000 emails per month) still benefit from dedicated IPs because they have enough volume to build and maintain a solid IP reputation on their own terms.
• Everyone should keep an eye on whether their sending IP has ended up on a blocklist, because that still causes real problems at Microsoft and enterprise filters.

If you want to check whether your IP or domain has any blocklist issues right now, our free Blocklist Checker takes about 30 seconds. It's worth a look before you assume all is well.