What are the pros and cons of shared IPs?
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A shared IP pools multiple senders onto the same sending address. Your reputation sits alongside everyone else the ESP has put in that pool, for better and for worse.
The main advantages: no warmup required. The IP already has sending history, so you can start sending at volume without the weeks-long ramp-up that a fresh dedicated IP demands. Lower cost, since the infrastructure is shared. Good fit for smaller senders who don't have the volume to sustain an IP's reputation on their own. And your ESP takes care of pool health monitoring, so you don't have to.
The downsides are real, though. If a bad actor in the same pool hammers a spam trap or triggers a complaint spike, your mail gets caught in the fallout even if your own practices are clean. You have limited visibility into what's happening at the pool level. Troubleshooting deliverability issues gets harder because the problem might originate with someone you've never heard of.
Most ESPs manage shared pools carefully and will remove bad actors quickly. A well-managed shared IP often outperforms a poorly-managed dedicated one. The quality of the pool matters as much as whether it's shared or dedicated.
For senders under roughly 100,000 emails per month, shared IPs are usually the right call. Above that threshold, dedicated IP territory starts to make more sense.
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