Shared IP
An IP address shared among multiple email senders, where everyone's reputation affects everyone else.
Shared IPs are the default for most email services and cold email platforms. Multiple senders use the same IP addresses, and the collective sending behavior determines the IP's reputation.
Advantage: no IP warming needed, lower cost, and benefit from the pool's existing reputation. Disadvantage: if other senders on your shared IP abuse it, your deliverability suffers.
Reputable platforms (Instantly, Smartlead) maintain their shared IP pools carefully. For most cold emailers sending under 5,000 emails/day, shared IPs are perfectly fine.