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. Doing this right helps you avoid spam folders and ensures high deliverability over time.
💡 Tip: New domains or ones that haven’t been actively used for bulk sending should always go through a warm-up phase.
Before You Begin
Here's a short recap of what you’ll do in Omnisend:
Export your subscribed contacts
Split them into smaller, daily batches
Re-import each batch, creating a specific segment
Send emails gradually over 20+ days
Monitor performance and adjust as needed
Step 1: Export Your Subscribers
To warm up your domain, first check if your audience is already uploaded to Omnisend (Audience → Contact list). If it is not uploaded yet, you can move directly to Step 2 to work on your csv files. If it’s already in Omnisend, you’ll need to export your subscribed contacts first.
If you already have engagement metrics like opens & clicks for your customer base in Omnisend, target the most engaged audiences first (create segments based on engagement filters).
During the first stages of the warmup, you will need to focus on sending emails only to your most engaged audience. After the first week, you can start mixing engaged with unengaged contacts, but make sure the ratio is always in favor of the engaged ones.
If you are a new sender without engagement metrics yet, proceed with the steps described below.
Here’s how to export your subscribers from Omnisend:
Go to Audience → All contacts.
Click Export → New Export.
Under “Select contacts to export,” choose contacts by email subscription status → Subscribed.
Click Export and download the CSV.
This file is your clean, permission-based audience — the best starting point for warming up.
Step 2: Split the File Into Daily Batches
Now split your exported list into smaller batches so you can slowly ramp up the sending volume day by day.
You can use Google Sheets, Excel, or other online CSV splitter tools. Each batch will be used for one day’s campaign. You only need email addresses in your future files; everything else can be removed from the lists.
👇 Simple Example (Manual Split in Excel or Google Sheets)
Let’s say you exported 10,000 contacts and you’re following the Medium Plan (different plans are described below), which starts with 1,000 emails on Day 1.
Here’s what you 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.
Example Warm-up Plan
Here’s an example 20-day warm-up plan crafted by our deliverability experts. It has three levels of sending volume increase. Choose the one that best matches your list size and risk tolerance.
For smaller audiences, maintain the ratios and calculate your audience sizes 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 — it balances safety and speed.
Step 3: Re-import Batches as Warm-up Segments
For each CSV batch:
Go to Audience → Add or update contacts → Import contacts from a file.
Upload the file.
During the import map only the Email field.
Create a specific segment for each file like:
Warm-up day 1Warm-up day 2Warm-up day 3etc.
Review and import.
📌 These segments let you target each group separately when sending. If you need more guidance for importing the files, please refer to our user guide.
Step 4: Send Daily Campaigns to Each Group
Each day, send a campaign to the matching segment (e.g., send to Warm-up day 1 on Day 1).
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 the sender's reputation.
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 (you can segment them and export this segment).
If you’re uncertain about which plan to follow or if anything feels off during your warm-up, please reach out to our team anytime via live chat or email us at [email protected]. We are available 24/7 to help.