Introduction
“Dedicated” sounds better, but dedicated IP vs shared IP is a trade-off, not a trophy. In email deliverability, control can help or hurt depending on your volume and sending behavior.
This guide is for SaaS and development teams sending transactional emails such as OTPs, password resets, receipts, and notifications. You’ll learn when shared IPs are the safer default, when a dedicated IP is worth it, and how to upgrade without causing a deliverability dip.
You’ll also get a rollout plan with baseline metrics, traffic segmentation, warmup, monitoring, and rollback. That is the difference between “we upgraded” and “we broke password resets.” To prepare before any IP changes, you can review setup and sending guidance in MailCub Documentation and test your sending flow with the Transactional Email product.
Quick Answer
- Stay on shared IP if your volume is low, irregular, or you cannot run a warmup plan.
- Upgrade to a dedicated IP if you need reputation isolation, predictable sending, or customer allowlisting.
- A dedicated IP can underperform early if you ramp too fast or send in bursts because the IP starts cold.
- Split transactional and marketing streams to protect critical emails from reputation swings.
- Monitor bounces, throttles (deferrals), complaints, and domain-level performance during the transition.
Why It Matters
For SaaS, email deliverability is product reliability. If OTPs and password resets fail, users churn and support volume increases.
IP choice affects reputation signals at mailbox providers. Shared IP pools spread risk and are often stable for smaller senders. Dedicated IPs isolate reputation, but they also make you fully responsible for it.
The wrong decision does not just affect marketing. It can break the emails users rely on to log in and pay.
Dedicated IP vs Shared IP: What Actually Changes
Shared IP (pool) means you share sender reputation with other customers of your provider. Good providers manage pools aggressively, but you still do not fully control neighbor behavior.
Dedicated IP means your sending reputation is mostly yours. That is useful when you have consistent volume and want clean separation. It is risky when you are low-volume or bursty because the IP stays cold.
Rule of thumb: control is valuable only if you can maintain it with steady, healthy sending.
Dedicated IP vs Shared IP: Upgrade Decision Framework
Use this framework to decide without guesswork. If you are unsure, shared IP is often the safer starting point until your sending patterns and monitoring are stable.
When each option is usually better
| Signal | Shared IP is usually better | Dedicated IP is usually better |
|---|---|---|
| Volume | Low or moderate | High |
| Pattern | Spiky / irregular | Predictable daily sends |
| Team readiness | No warmup/monitoring bandwidth | Can run warmup + alerts |
| Isolation need | Not critical | Required (reputation separation) |
| Customer requirements | No allowlisting needs | Some customers require fixed IPs |
| Risk tolerance | Prefer stable defaults | Can tune and iterate |
Step-by-step Upgrade Plan
1) Establish baseline metrics before switching anything
Pull 14–30 days of:
- delivery rate
- hard vs soft bounces
- complaints (if available)
- deferrals/throttling
- top recipient domains (gmail/outlook/yahoo/corporate)
Baseline first so you can prove improvement or detect regression quickly.
2) Segment traffic into streams
Do not treat all email the same. Create streams such as:
- Stream A: OTP / password reset (highest priority)
- Stream B: onboarding / product notifications
- Stream C: marketing (if applicable)
This prevents risky traffic from affecting critical transactional mail.
3) Confirm DNS and authentication are solid
Before any IP upgrade, confirm:
- SPF, DKIM, and DMARC are correct for your sending domain
- your From domain aligns with authentication
- your sending host has valid rDNS/PTR if you manage infrastructure directly
A dedicated IP will not fix broken fundamentals. It only makes failures more clearly yours. You can verify configuration and sending setup steps in MailCub Documentation.
4) Warm up the dedicated IP (slow, consistent ramp)
Warmup is a controlled ramp of daily volume. Start with your healthiest recipients and most predictable traffic. Increase slowly and keep the cadence steady. Avoid sudden spikes from a new IP.
If your sending is naturally bursty, consider staying on a shared pool or using a hybrid approach, where bursty or low-volume traffic stays shared and dedicated IP traffic is used only once volume is stable.
5) Roll out like a canary (percentage-based routing)
Treat the IP change like a production deployment. Start with 5–10% of traffic on the dedicated IP. Compare outcomes against your baseline and a shared IP control group. Increase only if metrics remain stable.
This is how you avoid an overnight breakage in login or billing flows.
6) Add monitoring and alerts so you catch problems early
At minimum, alert on:
- bounce rate spikes (windowed)
- deferral/throttle spikes (windowed)
- complaint spikes (windowed)
- domain outage patterns (one domain failing more than others)
Also store message IDs and log references so support and engineering can debug quickly. Use MailCub Documentation to set up message IDs, delivery logs, and basic alert rules, and use the Transactional Email service for sending, logs, and event tracking.
Common Mistakes
- Moving to a dedicated IP to “fix deliverability” without fixing authentication, content, or list hygiene first.
- Switching all traffic at once with no canary and no rollback.
- Warming up with bursty campaigns instead of steady transactional streams.
- Using a dedicated IP with too little volume to establish stable reputation.
- Mixing marketing and transactional traffic on the same dedicated IP without stream separation.
- Not tracking deferrals and throttles, which are early warning signals.
Troubleshooting When a Dedicated IP Looks Worse
Issue: Deliverability drops right after switching
This often happens when the IP is cold or ramped too quickly.
Action: Reduce volume, stabilize cadence, prioritize engaged recipients, and extend the warmup window.
Issue: Deferrals or throttles spike on one domain
This usually indicates per-domain rate limits or reputation signals.
Action: Apply per-domain pacing and backoff. Keep retries bounded and steady.
Issue: Spam placement increases
Check authentication alignment, rDNS/PTR (if self-managed), content patterns, and whether the stream mix changed.
Action: Revert risky traffic (especially marketing) off the dedicated IP and keep transactional mail stable while reputation improves.
FAQ
Is a dedicated IP always better than a shared IP?
No. Dedicated IPs give isolation and control, but they require warmup and consistent sending. Shared IPs are often safer for low or irregular volume.
When should a SaaS upgrade to a dedicated IP?
Upgrade when you need reputation isolation, have predictable daily volume, and can run warmup and monitoring.
What volume is enough for a dedicated IP?
Enough to send consistently every day and maintain reputation. If you only send occasional bursts, shared IP often performs better.
How long does IP warmup take?
It depends on your volume, recipient domains, and sending consistency. Plan for a gradual ramp, not a one-day switch.
Should transactional and marketing use separate IPs?
If you send both, separation is usually safer. It protects login and security emails from marketing complaints and reputation swings.
What metrics matter most during an IP transition?
Deferrals/throttles, hard and soft bounces, complaints, and per-domain performance. Always compare against your baseline.
What is the safest rollout plan?
Use canary routing (5–10%), monitor for 24–48 hours, then ramp gradually with a rollback switch ready.
Conclusion
A dedicated IP is a useful tool for teams with steady volume and a real need for isolation. If your sending is bursty or low-volume, a shared IP pool can be more forgiving and stable.
Upgrade safely by baselining metrics, segmenting streams, warming up steadily, and rolling out with a canary and rollback plan. That is how you improve deliverability without risking critical login flows.
To plan your transition, review setup and monitoring guidance in MailCub Documentation. If you want help with production sending and deliverability operations, start with the Transactional Email page and review MailCub Pricing for the right plan.