IP reputation is the trust score mailbox providers assign to the sending server's IP address itself, separate from domain reputation, based on that IP's history of complaints, bounces, and spam-trap hits across every sender who has used it.
IP reputation and domain reputation are not the same score, even though people use the two interchangeably. Domain reputation tracks how mailbox providers see a sending domain over time. IP reputation tracks the mail server's IP address itself, and it's shared across everyone else sending through that same IP if the sending infrastructure runs a shared pool.
Most cold outbound doesn't send enough volume to justify a dedicated IP, and a brand new dedicated IP with no sending history is closer to a liability than an asset, since it has nothing to lean on yet. A shared IP pool run by a decent sending infrastructure provider actually builds reputation faster in most cases, because a domain on that pool inherits some of the trust already built by every other well-behaved sender using the same IPs. A dedicated IP only earns its cost once a team sends enough volume to build and control that IP's reputation entirely on its own.
The two scores interact but don't substitute for each other. A domain with clean authentication and a long history of good behavior can still get dragged down by landing on a bad shared IP, and a spotless IP can't rescue a domain that's skipping SPF, DKIM, or DMARC. Both need to be healthy at once for mail to land in the inbox reliably.
Check IP reputation the same way as domain reputation: through blocklist lookups and inbox placement tests, not a single dashboard number. If a shared IP pool starts showing problems, the fix usually sits with the infrastructure provider rotating or cleaning the pool, not with anything a single sender can do to their own domain.
Teams assume a dedicated IP is automatically the safer, more professional option, the way a dedicated server sounds better than shared hosting. For cold outbound specifically it's often the opposite: a shared pool with real sending history outperforms a dedicated IP starting from zero. The dedicated option only wins at a volume most cold outbound programs never reach.
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