When you add a new sending domain or switch email providers, inbox services like Gmail and Yahoo treat you as a new sender. To build trust and ensure strong deliverability, Omnisend gradually increases your sending volume through an automatic warm-up process.
Continue reading to see how this process works and how Omnisend manages it for you.
Need more control over warm-up timing and volume? Use manual warm-up instead.
Before You Begin
Domain warm-up is required if you have 500+ subscribers and recently verified a dedicated sender domain or migrated to Omnisend.
Omnisend automatically splits your email campaigns: some emails are sent from your custom domain, others from our shared domain.
This split applies once per day: if you send multiple campaigns on the same day, only the first uses the split; subsequent campaigns send entirely from the shared domain.
You cannot use Campaign Booster or A/B testing until the warm-up completes.
Opting out risks poor deliverability – spam placement, blocks, and lower sales.
Progress can be tracked in Store settings → Domains.
Warm-Up Best Practices to Keep in Mind:
Always send to opted-in contacts only. Purchased or scraped lists harm reputation.
ISPs (Gmail, Yahoo, Outlook) trust engagement metrics, not brand names. Low engagement = junk folder.
Your domain reputation follows you across platforms. Skipping warm-up damages it permanently.
Recent opt-ins often engage more, but target your most active contacts first (opens/clicks in last 30–90 days).
Note: For greater control and the best deliverability results, we recommend using the manual warm-up process. Automatic warm-up is a good option if you prefer less manual work and don’t mind slightly lower performance.
About Email Warm-up
Warm-up builds your sender reputation by proving to mailbox providers that you send relevant, wanted emails.
What Affects Warm-Up Success
List quality: High bounce or complaint rates can delay or damage warm-up progress.
Engagement: Opens and clicks signal trust and help establish a positive reputation.
Content quality: Spam-trigger words or poor formatting increase the risk of filtering.
Note: During warm-up, some emails may land in spam folders, especially when migrating platforms. This is expected while providers like Gmail, Yahoo, and Outlook adjust to your new sending patterns.
Warm-up Benefits
Track performance early: Monitor key metrics like opens, clicks, and bounces from the start to improve your email strategy.
Simplify future sending: A strong sender reputation reduces deliverability issues, so you can focus on growing your business, not fixing problems.
Build ISP trust: Providers like Gmail and Outlook assess your sending behavior, content, and engagement to determine inbox placement.
Improve content effectiveness: Warm-up is a great time to test and refine your content by identifying which messages generate the most (or least) engagement.
Exclude disengaged contacts: Removing inactive subscribers boosts ROI, improves deliverability, and helps reduce sending costs.
⚠️ Risks of Skipping Warm-Up:
Emails may be blocked entirely;
Messages may be delivered right to spam folders;
Long-term damage to your domain reputation.
How to Set Up Automatic Warm-Up
Step 1: Verify your custom domain.
Go to Store Settings → Domains → Add domain and follow the steps in our dedicated guide to verify your domain.
Step 2. Assign domain in use.
In Store Settings → Domains, navigate down to Domain in use. scroll down to the Domain in use section. From the drop-down menu, select your custom domain for use in campaigns and automations.
Step 3: Choose automatic warm-up.
After assigning your domain, you'll see a popup to select your warm-up strategy. Click Warm up automatically.
Step 4. Monitor the warm-up process.
Once you select automatic warm-up, you can track its progress in Store settings → Domains.
💡 You'll also see warm-up progress during the Review step when creating campaigns.
How Automatic Warm-Up Works
Omnisend automatically splits your audience for each campaign during warm-up.
A portion of your emails is sent from your custom domain, while the rest is sent from Omnisend's shared domain.
Omnisend will gradually increase the percentage of emails sent from your domain.
Omnisend splits your audience automatically based on recent subscription date (most engaged contacts first).
Here's how the volume of emails sent from your domain increases:
Day | Campaign | Volume per campaign |
Day 1 | Campaign 1 | 500 |
Day 2 | Campaign 2 | 1000 |
Day 3 | Campaign 3 | 2000 |
Day 4 | Campaign 4 | 4000 |
Day 5 | Campaign 5 | 8000 |
Day 6 | Campaign 6 | 12000 |
Day 7 | Campaign 7 | 18000 |
Day 8 | Campaign 8 | 25000 |
Day 9 | Campaign 9 | 35000 |
Day 10 | Campaign 10 | 50000 |
Day 11 | Campaign 11 | 65000 |
Day 12 | Campaign 12 | 80000 |
The gradual increase continues until 100% of emails are sent from your domain.
Example:
You send a campaign to 10,000 recipients on Day 1:
500 receive emails via your domain;
9,500 receive emails via Omnisend's shared domain.
On Day 2, you send to 5,000 recipients:
1,000 via your domain;
4,000 via Omnisend's shared domain.
When Automatic Warm-Up Ends
The automatic warm-up completes when:
The last 3 campaigns send 100% from your dedicated domain, OR
30 days pass (whichever comes first).
Once the warm-up is complete, it will be marked as Finished in Store settings → Domains.
💡 After your automatic warm-up ends, you can use Campaign Booster and A/B testing.
After Warm-UP
Once your automatic warm-up ends:
Continue monitoring metrics as an ongoing best practice every time you send campaigns. Regular monitoring ensures sustained deliverability and helps you catch issues early.
If your open rate stays ≥20% and spam rate ≤0.1%, you can maintain your current sending volume and cadence.
If metrics drop after warm-up, scale back temporarily by sending smaller campaigns to engaged contacts (segment them first).
💡 Best practice: Even after warm-up, avoid sudden volume spikes (e.g., jumping from 50K to 500K recipients). Gradual growth protects your sender reputation.
FAQ
Why do I need warm-up?
Warm-up is required for accounts with 500+ subscribers, newly verified domains, or when you migrate to Omnisend from another provider. It ensures emails reach inboxes and prevents spam filtering.
Do I need warm-up if I'm migrating from another platform but keeping the same domain?
Yes. Even if your domain stays the same, switching platforms means you're sending from new servers. Mailbox providers like Gmail and Yahoo treat you as a new sender on Omnisend's infrastructure and need to rebuild trust. Skipping warm-up can cause emails to land in spam or get blocked.
What happens if I send multiple campaigns in one day?
The automatic warm-up split applies to the first campaign only. Subsequent campaigns that day will be sent via the shared domain.
Can I use Campaign Booster or A/B testing during warm-up?
No. Both features activate only after the automatic warm-up completes.
What if I opt out of warm-up?
Opting out risks poor deliverability, spam placement, and blocks. We strongly recommend completing the warm-up.
How can I track the progress of the warm-up process?
Go to Store Settings → Domains → Domain warmup. The progress updates after each campaign.
Should I Use Automatic or Manual Warm-Up?
Manual warm-up is the recommended option for better control, higher deliverability, and a stronger sender reputation. It avoids shared domain traffic and gives you full visibility.
Automatic warm-up is suitable only if you need to send high volumes quickly and are willing to trade some deliverability performance for speed. It splits sending between your custom domain and Omnisend’s shared domain.
For the best long-term results, we strongly recommend manual warm-up.
Does warm-up apply to automation workflows?
No. Warm-up doesn’t apply directly to automations. Because automations send gradually, they don’t need warming up like bulk campaigns. However, we recommend warming up your domain with campaigns first before launching high-volume workflows.
If you have any questions or concerns about the warm-up process, please don't hesitate to contact our support team at [email protected] or via in-app chat for assistance.