IP warmup is the process of gradually increasing the volume of emails sent from a new or cold IP address over several weeks to build a positive sending reputation with ISPs before sending at full production volume. It is one of the most critical factors in achieving consistent inbox delivery — and skipping it is one of the most common and costly mistakes new senders make.
Why IP Reputation Matters
Every email you send travels from a specific IP address. Internet Service Providers (Gmail, Outlook, Yahoo, and others) track the sending behaviour associated with each IP they receive email from — including volume, complaint rates, bounce rates, and engagement. Based on this history, they assign a reputation score that determines how they treat email from that IP:
| IP Reputation Level | Typical Inbox Placement |
|---|---|
| High | Inbox — consistent delivery with minimal filtering |
| Medium | Inbox or Promotions tab — some filtering; throttling possible |
| Low | Spam folder — significant filtering and throttling |
| Bad | Blocked — email rejected outright; IP likely blacklisted |
What Happens Without Warmup
A brand-new IP address has zero reputation history. If you immediately send 10,000 emails from it:
- ISPs see a sudden burst of traffic from an unknown IP — a classic spam signal.
- Automated spam filters classify the IP as suspicious.
- 70–90% of emails land in spam or are rejected outright.
- The spike in delivery failures and spam complaints permanently damages the IP's reputation.
- Recovery can take weeks or months and may require migrating to a fresh IP.
Shared IP vs Dedicated IP — How Warmup Applies
| Shared IP (Default on MigoSMTP) | Dedicated IP | |
|---|---|---|
| What it is | Your emails share an IP address with other MigoSMTP senders who meet quality standards | You have exclusive use of a specific IP address — only your sending affects its reputation |
| Warmup needed? | Partial — MigoSMTP manages the shared IP warmup for the pool; you still need gradual ramp-up for your domain | Yes — full warmup required from zero |
| Reputation control | Shared — other senders on the pool can affect your delivery if they engage in poor practices (MigoSMTP actively monitors and removes bad senders) | Full control — your sending behaviour exclusively determines the IP reputation |
| Best for | Up to ~50,000 emails/month; starting out; lower-risk sending | Over 50,000 emails/month; high-volume senders; businesses where reputation isolation is critical |
| Cost | Included in standard plan | Additional monthly fee — contact Rackwave to request a dedicated IP |
How MigoSMTP Manages Warmup on Shared IPs
For accounts on shared IP pools, MigoSMTP actively manages the pool to protect all senders:
- Quality admission — only accounts with verified domains, passing authentication, and clean list practices are admitted to the shared pool.
- Monitoring — automated systems continuously monitor complaint rates, bounce rates, and sending patterns for all accounts on the pool.
- Isolation — accounts that damage the pool's reputation are removed from the shared pool and investigated before reinstatement.
- Progressive capacity — new accounts on the shared pool have their effective throughput limited initially and increased as they demonstrate clean sending.
Even on a shared IP, your domain reputation is your own — the warmup principles for your domain still apply regardless of IP arrangement.
Key Principles of IP Warmup
- Start slow, ramp gradually — every doubling of volume should be separated by at least 2–3 days of clean sending at the current level before increasing.
- Send to your best recipients first — engaged subscribers who open quickly send positive signals to ISPs that set the tone for the rest of the warmup.
- Consistency matters more than speed — sending 200 emails every day for two weeks is better for warmup than sending 1,000 twice in a week.
- Perfect list hygiene during warmup — any bounce or complaint during warmup has outsized negative impact on an IP with no existing reputation buffer.