Warming up your domain means gradually increasing the number of emails you send per day to build trust with inbox providers like Gmail, Outlook, and Yahoo. This process helps you avoid spam folders and improves your email deliverability over time.
Use this guide if you want the best deliverability results through a controlled, step-by-step warmup process.
💡 Manual warm-up is the recommended method for greater control and more consistent results.
Before You Begin
The manual warm-up starts with exporting your subscribed contacts, splitting them into smaller daily batches, and re-importing each batch as a segment.
You need to send emails gradually over 20+ days, monitoring performance and adjusting as needed.
Make sure your sender domain is verified. If not, set up your domain signature first.
💡Tip: New domains or ones that haven’t been actively used for bulk sending should always go through a warm-up phase.
Step 1: Export Your Subscribers
To begin warming up your domain, first check whether your audience is already uploaded to Omnisend. Go to Audience → Contact list to verify. If your audience isn’t yet uploaded, skip to Step 2 to begin working directly with your CSV files.
If your contacts are already in Omnisend and you have engagement data such as opens and clicks, focus initially on your most engaged subscribers. Create segments using engagement filters to identify this group.
During the early stages of warm-up, send emails only to highly engaged contacts. After the first week, you can begin to include unengaged subscribers, ensuring the majority of each send still targets engaged recipients.
If you're a new sender without engagement metrics, simply continue with the steps below.
To export your subscribers from Omnisend:
Go to Audience → Exports and click New Export.
Under “Select contacts to export,” choose contacts by email subscription status → Subscribed.
Click Export to download the CSV file.
This file is your clean, subscription-based audience; the best starting point for warming up your email domain.
Step 2: Split the File Into Daily Batches
Split your exported list into smaller batches to gradually increase your sending volume each day. Use Google Sheets, Excel, or a CSV splitter tool to divide the file. Each batch will be used for one day's email campaign.
You only need the email address column; remove any additional columns before saving your batches.
Example: Manual Split in Excel or Google Sheets
Let’s say you exported 10,000 contacts and you’re following the Medium Plan (see the table below), which starts with 1,000 emails on Day 1.
Here’s what to do:
Open the exported CSV in Google Sheets or Excel.
Keep only the “Email” column (delete the others if needed).
Select the first 1,000 rows (not including the header).
Copy and paste into a new sheet or file → Save as
warmup_day1.csv.
Select the next 1,500 rows → Save as
warmup_day2.csv.Continue with the next daily volumes from the warm-up table.
Choose Your Warm-Up Plan
Below is a sample 20-day warm-up plan created by our deliverability experts. It includes three ramp-up options: Conservative, Medium, and Aggressive. Choose the one that best fits your total list size and risk tolerance.
If your audience is smaller than the examples shown, keep the same daily growth ratios and adjust the sending volumes accordingly.
Day | Conservative Plan (35% increase rate) | Medium Plan (50% increase rate) | Aggressive Plan (65% increase rate) |
1 | 500 | 1,000 | 5,000 |
2 | 675 | 1,500 | 8,250 |
3 | 910 | 2,250 | 13,615 |
4 | 1,230 | 3,375 | 22,460 |
5 | 1,660 | 5,065 | 37,060 |
6 | 2,245 | 7,595 | 61,150 |
7 | 3,025 | 11,390 | 100,895 |
8 | 4,085 | 17,085 | 166,475 |
9 | 5,515 | 25,630 | 274,690 |
10 | 7,445 | 38,445 | 453,235 |
11 | 10,055 | 57,665 | 747,840 |
12 | 13,575 | 86,500 | 1,233,940 |
13 | 18,325 | 129,750 | 2,035,995 |
14 | 24,735 | 194,620 | 3,359,395 |
15 | 33,395 | 291,930 | 5,543,005 |
16 | 45,080 | 437,895 | 9,145,955 |
17 | 60,855 | 656,840 | 15,090,830 |
18 | 82,155 | 985,260 | 25,000,000 |
19 | 110,000 | 1,500,000 | 41,000,000 |
20 | 150,000 | 2,210,000 | 67,800,000 |
💡 Most users start with the Medium Plan since it balances safety and speed.
Step 3: Re-import Batches as Warm-up Segments
For each CSV batch you've created, go to Audience → Imports → Add or update contacts → Import contacts from a file.
Upload your file and map only the Email field during the import. When prompted, create a dedicated segment name for each batch, such as:
Warm-up day 1Warm-up day 2Warm-up day 3etc.
After reviewing, complete the import.
💬 These segments allow you to target each batch separately during your daily sends. For detailed steps on importing contacts, refer to the dedicated guide.
Step 4: Send Daily Campaigns to Each Group
Send one campaign per day to the corresponding segment. For example, send to Warm-up Day 1 on Day 1, Warm-up Day 2 on Day 2, and so on.
Tips for Better Results
Use value-driven, non-promotional content at first (tips, brand intro, helpful info).
Gradually increase frequency and audience size as you build your sender's reputation.
Avoid sending at the top of the hour (e.g., send at 10:12 AM instead of 10:00 AM) to reduce inbox competition and improve deliverability.
Monitor Performance
After each send, check your Reports → Campaigns → Campaign Performance in Omnisend. Pay close attention to:
Open rate
Click rate
Failed delivery rate
Marked as spam rate
Unsubscribe rate
If your open rate drops significantly or spam complaints rise, pause the process and send a smaller batch to highly engaged users (segment them first).
After Warm-Up
Once you complete the 20-day plan:
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're ready to send to your full audience.
If metrics drop, extend warm-up by repeating smaller batches to engaged contacts.
FAQ
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 with your domain. Skipping warm-up can cause emails to land in spam or get blocked.
Can I skip days during warm-up?
That is not recommended as consistency is key. Mailbox providers closely monitor your sending patterns, and irregular schedules or skipped days can negatively impact your sender reputation. Stick to your warm-up plan by sending at roughly the same time each day, three times per week.
If you must skip a day, resume your schedule as planned without increasing the volume to compensate.
Should I use automatic or manual warm-up? What’s the difference?
Manual warm-up is always the preferred method for better deliverability and sending reputation. It gives you full control and avoids splitting traffic through shared domains, which have lower performance due to their nature.
Automatic warm-up is an option only if your brand cannot afford to slow down sending and is okay with compromising quality and results to maintain high volume quickly. Omnisend automatically splits your audience, sending some emails through our shared domain and others through your custom domain.
We always recommend the manual warm-up for the best control, quality, and long-term deliverability. The automatic warm-up should only be used if your brand cannot afford to slow down sending and is willing to compromise slightly on quality and results in order to maintain high volume.
Do I need to warm up if I only have 300–500 subscribers?
If you have fewer than 500 subscribers, the warmup is not essential. Warmup becomes more critical as your contact list grows above 500 subscribers.
If you’re uncertain about which plan to follow or if anything feels off during your warm-up, reach out to our team anytime via live chat or email us at [email protected]. We are available 24/7 to help.