Old rule of thumb: dedicated IP above 100k emails/month. That number is now much higher — and for most senders, shared is actually better.
What changed
Google and Yahoo's 2024 bulk-sender rules made domain reputation more important than IP reputation. Providers built better shared-IP pools with active reputation monitoring. And the operational load of running your own IP (warming, monitoring, managing blacklists) hasn't gone down.
When shared wins
- Below 500k emails/month — you don't have enough volume to drive your own IP's reputation.
- Bursty sending — a dedicated IP with low steady volume looks suspicious to receivers.
- Mixed transactional + marketing on the same domain — a shared pool provides better base reputation.
- You don't want to manage IP warmup, monitoring, and troubleshooting.
When dedicated makes sense
- > 500k messages/month with predictable volume.
- Complete control over reputation (no exposure to other senders in the pool).
- Regulatory / compliance reasons that require known-source IPs.
- Deliverability team on staff who can react to reputation changes.
The middle path
Most established SaaS products land here: shared IP for transactional email (where volume is predictable and reputation is domain-driven), dedicated IP for marketing blasts (where volume spikes and IP reputation matters more). Two subdomains, two IPs, isolated reputation.
The math
Dedicated IP costs $50–$300/month depending on provider. To justify it, you need enough volume that a shared-pool issue would cost more than that. At 500k msgs/mo, a one-day pool degradation might delay 15k messages — a real problem. At 50k msgs/mo, it's a 1,500-message delay — measurable but not catastrophic.
Start shared. Move to dedicated when you have the volume, the volatility, and the ops capacity to run it well.