Email warmup mimics natural human conversations between email accounts to build your sender reputation with email service providers (ESPs).
The Warmup Pool
When you enable warmup, your account joins a pool of other Instantly users who have also enabled the feature. Here's what happens:
Your account sends warmup emails to other users in the pool
Other users' accounts send warmup emails to you
All warmup emails are automatically opened
A high percentage receive replies with positive sentiment
Why This Improves Deliverability
These interactions send positive signals to Gmail, Outlook, and other email providers:
Engagement signals – High open and reply rates demonstrate that your emails are valued
Reputation building – Consistent positive interactions establish your account and domain as legitimate
Trust establishment – Email providers learn to trust emails from your sending domain
When you connect a sending account to Instantly, warmup also warms up your SMTP sending server and IMAP receiving server to ensure your entire email infrastructure builds a positive reputation.
As your sender reputation improves, your cold outreach emails are more likely to:
Land in recipients' primary inboxes (not spam)
Get opened by your target audience
Generate genuine replies from prospects
Beyond improving deliverability, warmup helps your email accounts:
Stay active and healthy for longer periods
Avoid being flagged or suspended by email providers
Reduce the risk of "burning through" accounts due to poor reputation
The Bottom Line
Email warmup improves the deliverability of your cold email campaigns by creating a history of positive, human-like email interactions within the Instantly user pool. This builds trust with email providers and increases the likelihood that your outreach emails will reach their intended recipients.
Think of it as you emailing back and forth with your friends - on autopilot.
Troubleshooting Warmup Issues
Warmup Emails Are Going to Spam
Warmup Emails Are Going to Spam
It's completely normal for warmup emails to land in spam initially. This is actually part of the warmup process.
New connections – As your accounts warm up, we continuously introduce new accounts to your warmup pool
No prior history – Your accounts interact with recipient accounts they've never emailed before
Building reputation – New accounts start with lower sender reputation, so some warmup emails may go to spam initially
Our system automatically moves warmup emails from spam to the inbox. This process is what builds your sender reputation over time. It's recommended to follow these best practices:
Verify DNS setup – Ensure all DNS records (MX, SPF, DKIM, DMARC) are properly configured
Keep the recommended limit – Stick to 10 warmup emails per day for new accounts
Don't rush the process – Never enable "Disable slow warmup" for new accounts
Allow sufficient time – Wait at least 2 weeks before using accounts for campaigns
How to know if my account is ready for campaign?
How to know if my account is ready for campaign?
To check if your account is ready for campaigns, verify these two key requirements:
Warmup Duration: Your account should be warmed up for at least 2 weeks. Click on the email account or eyeball icon next to the flame to see how long it's been warming up.
Health Score: Warmup health score should be above 90%. Check this in your Email Accounts dashboard under the Health score column
Exception: Pre-warmed accounts purchased from Instantly can be used in campaigns from day 1.
What is warmup health score?
What is warmup health score?
The warmup health score shows how well your email account is performing based on warmup activity over the past 7 days.
It measures how many of your warmup emails landed in the inbox versus spam folders. For example, if your account sends 70 warmup emails over 7 days and 3 land in spam, your health score would be about 95.7%.