IP reputation is the part of sender reputation attached to the IP address of the server that sends an email. Blocklists, such as Spamhaus and Barracuda, mostly list IP addresses.
Shared or dedicated
- Shared IPs (Google Workspace, Microsoft 365 and most email services): many senders use the same addresses, and the provider looks after their reputation. You can't damage them much on your own, and you don't need to warm them.
- A dedicated IP: only you send from it, so its reputation is entirely yours. Useful at very high volume; a liability for a few thousand emails a day.
For cold email
With mailboxes on Google Workspace or Microsoft 365, IP reputation is largely handled for you, and domain reputation is what you build. If you do send from your own IP, set a PTR record, warm the IP up slowly and check it against blocklists with the free blacklist checker.