Shared IPs pool many senders' reputations together. Dedicated IPs isolate one sender's reputation. Both have appropriate use cases; the decision is driven by volume, vertical and reputation dynamics.
When shared is appropriate
Low daily volume — below roughly 50,000 recipients per day — usually cannot sustain the reputation signal a dedicated IP needs. Providers evaluate reputation partly on volume: too little data and the IP falls into a default treatment that is often worse than sharing with well-behaved senders.
When dedicated is appropriate
Sustained volume above 100,000/day. Sensitive verticals where a noisy neighbour would sink you. Regulatory or brand attribution requirements. Multi-brand programmes where cross-attribution would be harmful.
Common myths
- 'Dedicated IPs get you into the inbox.' False. Dedicated IPs isolate reputation; content, list and authentication still determine placement.
- 'More IPs are always better.' False. Under-utilised IPs never warm properly.
- 'Aged IPs come with reputation.' Mostly false. Provider reputation follows the current sender's behaviour more than IP age.
Related articles
- SPF ExplainedHow Sender Policy Framework works, how to author a record correctly, and how to avoid the common failure modes.
- DKIM ExplainedDomainKeys Identified Mail — how signing works, selector strategy, key length and rotation, and what DKIM cannot do.
- DMARC GuideHow DMARC ties SPF and DKIM together, staged policy rollout from monitor to reject, and how to use aggregate reports.
- Google Postmaster GuideHow to set up Postmaster Tools, what each metric means, and how to interpret the reputation graph.
- PowerMTA OptimizationVMTA design, queue tuning, per-domain policy, and the configuration mistakes that quietly cost inbox rate.
- IP Warm-upHow to warm a new IP without wasting weeks or torching reputation. Volume curves, segmentation, and when to stop.