IP and domain warmup
IP and domain warmup is the process of gradually increasing campaign volume week over week on a new IP address or domain. This helps establish a positive sending reputation with mailbox providers and targets engaged users.
Start your campaign by focusing on your most reliable subscriber data. Add older data and less engaged users to later segments of the warmup.
For every new domain used with the Infobip web interface, there is an automated IP and domain warmup. For new domains used over API, some accounts will also undergo automated warmup.
To ensure successful IP and domain warmup and boost deliverability:
- Clean email databases by removing invalid emails.
- Only send emails to recipients who have signed up or opted in.
- Implement an email verification process during signup.
- Do not purchase lists from scrape sites.
Why IP and domain warmup matters
Mailbox providers such as Gmail, Yahoo, and Outlook closely monitor traffic from new senders. A new sender is typically defined by a previously unused IP address or domain. Sending high volumes from a cold IP or domain without a warmup can trigger spam filters, blocks, or delivery delays.
Warming up your domain establishes credibility over time. Positive engagement, such as opens and clicks from valid recipients, contributes to a healthy reputation. Sending to invalid or inactive addresses can degrade reputation, limit deliverability, and result in throttling or filtering.
Daily email traffic
To ensure high deliverability and protect your domain reputation, it is important to understand how email traffic is managed. Infobip tracks and regulates your daily email volume through key traffic metrics. These metrics guide the automated warmup process and ensure a stable, consistent sending pattern, especially when using a new domain.
Main types of traffic metrics:
- Base traffic: The maximum number of emails sent by a particular sending domain in a daily (24-hour) window, calculated over the last 30 days. If no emails are sent in the last 30 days, the automated warmup process restarts.
- Targeted daily traffic: Set when you add or configure a new domain. This value should match the amount of consistent traffic (emails per day) you want to send from the domain. It also acts as a threshold to decide when a domain is considered warmed up.
- Sending speed: Calculated automatically during automated warmup. It ensures there is a small pause between each email to provide better overall delivery.
Automated warmup
Automated domain warmup is the process of gradually increasing the daily sending volume of a newly registered domain to establish and maintain a strong sender reputation. This helps prevent spam filtering and protects both the domain and IP address reputation.
Smart warmup
Smart warmup automatically adjusts sending limits based on delivery results, helping you scale faster when performance is strong.
How it works:
- Fast warmup (50% increase): Applied if your domain sends more than 500 emails and maintains a delivery rate of 98% or higher.
- Moderate warmup (40% increase): Triggered if your domain sends at least 500 emails with a delivery rate between 96% and 98%.
- Slow warmup (30% increase): Used when the delivery rate falls below 96%.
Key considerations during automated warmup
- New domains start with:
- Base traffic: 0
- Initial sending speed: 500 emails per day
- Only one campaign from the sending domain can run at a time during warmup.
- A domain is considered warmed up once its base traffic reaches two-thirds of its targeted daily traffic.
- If a domain sends fewer emails consistently over 30 days, the warmup process may restart and reduce sending speed.
API automated warmup
Some sender domains created through the API must also go through automated warmup. The warmup process ensures that new domains gradually scale their daily email volume, protecting sender reputation and improving deliverability.
Warmup logic (API)
- Starting volume: 500 emails per day
- Growth rate: Previous day’s sent volume plus 40%
- Warmup target: 1,000,000 emails per day
Volume limit
While the initial sending volume is capped at 500 emails, the daily volume limit from day two onward depends on the number of emails successfully sent the previous day, increased by 40%. This dynamic adjustment ensures a gradual and reputation-friendly increase in traffic.
The volume limit changes dynamically based on the previous day’s performance:
| Domain | Day 1 sent | Day 2 limit |
|---|---|---|
eatfruiteveryday.com | 500 emails | 500 + 40% = 700 |
eatvegetableseveryday.com | 300 emails | 300 + 40% = 420 |
What happens to excess emails?
Emails exceeding the daily limit are not discarded but put into retry with error code 6050 (SENDER_WARMUP). These retries are attempted for up to 48 hours, as with other email traffic.
Manual warmup (API)
In some cases, a manual warmup process is required for IP or domain configuration via API. If this applies to your account, contact your account manager or Support for guidance on setting up and managing the warmup manually.
To maintain high deliverability and gradually build a strong sender reputation, follow a 14-day warmup schedule.
Suggested daily sending volume:
| Day | Emails per day |
|---|---|
| 1 | 500 |
| 2 | 700 |
| 3 | 1,000 |
| 4 | 1,400 |
| 5 | 2,000 |
| 6 | 2,800 |
| 7 | 4,000 |
| 8 | 5,600 |
| 9 | 8,000 |
| 10 | 11,200 |
| 11 | 16,000 |
| 12 | 23,000 |
| 13 | 33,000 |
| 14 | 50,000 |
Engagement guidelines during warmup
- Days 1-14: Only send to your most engaged subscribers.
- Weeks 3-4: Expand to users who engaged within the last 60 days.
- First 45 days: Avoid sending to users who have not opened or clicked emails in the past 90 days.
If you plan to send over 10 million emails monthly, contact Support for a customized warmup plan and further recommendations.