What is the best practice for warming up a new email sending domain for a small list of cold contacts?
Matthew Whittaker
Co-founder & CTO, Suped
Published 11 Jun 2025
Updated 19 Aug 2025
6 min read
Warming up a new email sending domain, especially for a small list of cold contacts, requires a very careful and methodical approach. Unlike warm lists, cold contacts may not have recent engagement with your brand, making them more susceptible to disengagement signals like unsubscribes or spam complaints.
The goal of domain warming is to build a positive sender reputation with internet service providers (ISPs) like Gmail and Yahoo. ISPs observe your sending patterns, bounce rates, spam complaint rates, and engagement metrics to determine if your emails are legitimate and wanted. A new domain has no history, so it starts with a neutral, often suspicious, reputation.
Ignoring the warm-up process for cold contacts can quickly lead to your emails being flagged as spam, ending up in junk folders, or even having your domain added to an email blocklist (or blacklist). This can severely hinder your email deliverability and overall marketing efforts. It's crucial to approach this strategically to ensure your messages reach the inbox.
Setting the foundation for warm-up
Before you send your first email, a solid foundation is essential. This involves preparing your domain and email setup to maximize the chances of a successful warm-up. Neglecting these initial steps can lead to immediate red flags for ISPs, regardless of your sending volume.
First, ensure your new domain isn't too new. Many experts recommend letting a domain age for at least 30-90 days before sending any emails. This natural aging process helps establish a baseline level of trust with ISPs, making your new domain appear less suspicious. Additionally, set up a simple website or redirect for the new domain. This provides legitimacy to postmasters who might investigate your sending domain, reassuring them that it belongs to a real company.
Crucially, implement all necessary email authentication protocols. This includes SPF (Sender Policy Framework), DKIM (DomainKeys Identified Mail), and DMARC (Domain-based Message Authentication, Reporting, and Conformance). These records verify that your emails are genuinely from your domain and haven't been tampered with, significantly boosting your sender reputation and helping to prevent spoofing. Properly configured DMARC, SPF, and DKIM records are non-negotiable for deliverability.
Essential technical setup
SPF record: Authorizes specific IP addresses and domains to send email on your behalf. Create a TXT record for your domain.
DKIM record: Adds a digital signature to your outgoing emails, allowing recipients to verify that the email was sent by the domain owner. You will typically receive this from your Email Service Provider (ESP).
DMARC record: Builds upon SPF and DKIM, telling receiving servers what to do with emails that fail authentication. Start with a p=none policy to monitor without affecting delivery.
Sample SPF record
SPF TXT RecordDNS
v=spf1 include:_spf.example.com ~all
Finally, before sending, verify your cold contact list. Even if contacts provided consent at an event, stale or incorrect addresses can lead to hard bounces and spam traps. Use a reputable email verification service to clean your list, removing invalid or risky emails. This protects your emerging sender reputation from immediate damage.
The gradual warm-up strategy
Warming up for a small list of cold contacts means starting extremely slow and gradually increasing your volume. The key is to mimic organic sending behavior, not a sudden blast of emails. ISPs are wary of new domains that immediately send large volumes, as this is a common tactic for spammers.
I recommend starting with a very small batch, perhaps as few as 10-20 emails on the first day. You should send these to the most engaged or likely-to-engage contacts within your small cold list. Since the contacts are 'cold,' you'll need to clearly state how you acquired their information, for instance, by mentioning the specific event or show where they opted in. This transparency helps build trust and reduces the likelihood of spam complaints.
Gradually increase your sending volume each day or every few days. The rate of increase should be conservative, perhaps doubling the volume every 2-3 days, depending on how recipients respond. For a list of 1000 cold contacts, this process could take a few weeks to a month. Focus on encouraging positive engagement such as opens, clicks, and replies. This positive interaction signals to ISPs that your emails are valuable and wanted. Conversely, a high bounce rate or spam complaint rate, even from a small list, can significantly damage your sender reputation.
Here's a sample warm-up schedule, but remember to adjust it based on your list's engagement and any feedback you receive from ISPs:
Day
Daily volume
Cumulative volume
Notes
1-2
10-20
10-40
Send to most responsive; mention consent source.
3-4
30-50
40-90
Monitor engagement closely, look for opens/clicks.
5-7
60-100
90-190
Continue increasing if engagement is positive. Consider a soft call-to-action.
Monitoring your domain's performance during the warm-up period is as crucial as the sending itself. Without proper oversight, you risk undermining your efforts and ending up on a blocklist (or blacklist).
Actively track your key email metrics. Pay close attention to your open rates, click-through rates, bounce rates (both soft and hard), and unsubscribe rates. For cold contacts, a high bounce rate is particularly problematic and indicates a need to clean your list further. Any spike in spam complaints should immediately trigger a pause in sending and a reassessment of your content or list quality.
Key metrics to monitor
Open rate: Aim for a minimum of 10-20% for cold outreach, higher for warm lists.
Click-through rate (CTR): Indicates content relevance and engagement.
Bounce rate: Keep this as low as possible (<2%). High bounces indicate poor list hygiene.
Spam complaint rate: Must be below 0.1% (1 in 1,000 emails). Even 0.05% is risky.
Tools for monitoring
Google Postmaster Tools: Essential for tracking your reputation with Google, including spam rates, IP reputation, and domain reputation. Set this up from day one.
Your ESP's analytics: Provides real-time data on opens, clicks, bounces, and complaints.
Even after you've reached your desired sending volume for the cold list, continue to monitor these metrics regularly. Sender reputation isn't a one-time achievement, but an ongoing process. If you pause sending for a long period, you might need to re-warm your domain, though typically at a faster pace than the initial warm-up.
Final thoughts on warming up your domain
Successful domain warm-up for a small list of cold contacts hinges on patience, consistency, and vigilant monitoring. Starting small, providing clear context in your emails, and ensuring technical setup are foundational steps.
Remember, the goal is to prove to ISPs that you are a legitimate sender and that your recipients want your emails. By following these best practices, you can effectively build a strong sender reputation for your new domain, ensuring your messages land in the inbox, not the spam folder.
Views from the trenches
Best practices
Always have a website or a redirect for your new sending domain to show legitimacy to ISPs and postmasters.
Clearly state how you obtained the recipient's email address in your initial communications, especially for cold contacts.
Implement and correctly configure SPF, DKIM, and DMARC from day one to authenticate your emails.
Common pitfalls
Sending a large volume of emails too quickly from a brand new domain, which can trigger spam filters.
Not verifying your cold contact list, leading to high bounce rates and spam traps that damage reputation.
Failing to set up email authentication protocols like SPF, DKIM, and DMARC before starting your sending.
Expert tips
Consider letting a new domain age for at least 30-90 days before starting any email sending campaigns.
If your new domain is linked to an existing trusted domain (e.g., via DKIM keys), it might reduce the initial risk.
Don't leave a newly warmed-up domain unused for long periods, as its reputation can degrade and require re-warming.
Marketer view
Marketer from Email Geeks says Gmail is particularly sensitive, so follow their guidelines closely, as they generally apply to other providers.
2017-09-28 - Email Geeks
Marketer view
Marketer from Email Geeks says for tiny lists, Google suggests starting with small batches, waiting a few hours, and then repeating the process several times.
Gmail
and 
Yahoo. ISPs observe your sending patterns, bounce rates, spam complaint rates, and engagement metrics to determine if your emails are legitimate and wanted. A new domain has no history, so it starts with a neutral, often suspicious, reputation.
Essential for tracking your reputation with Google, including spam rates, IP reputation, and domain reputation. Set this up from day one.
