If you’re reading this, you’re probably either struggling to get your emails out of the spam folder, or you’re smart enough to research domain warm-up before launching your cold email campaigns. Either way, you’ve come to the right place.
After warming up over 4719 email domains in the past year for our email outreach and to funnel our clients at Outbound Master, we have perfected the process to a science. We’ve seen what works, what fails, and most importantly, what has changed in 2025. No fluff, no theory—just a practical guide that has worked consistently across different industries and email service providers.
Let’s dive into exactly how to warm up your email domain properly.
Understanding Email Domain Warm-up
After handling many email domains, I can tell you that understanding warm-up isn’t just some technical checkbox. It’s the difference between your emails hitting inboxes or dying in spam folders.
Why Email Warm-up Is Non-Negotiable in 2025
Here’s what most “experts” won’t tell you: In 2025, ISPs have gotten good at spotting unwanted emails. We’re talking AI-powered filters that analyze your sending patterns down to the hour. After warming up domains for clients across every major industry, we’ve watched ISPs evolve from simple spam filters to sophisticated trust analyzers.
Let me break down what’s actually happening behind the scenes:
The Evolution of Email Deliverability
Remember when you could just start sending emails and hope for the best? Those days are dead and buried. Today’s ISPs are looking at:
- Your sending velocity (and they’ll throttle you faster than ever if you mess this up)
- The way real humans interact with your emails (or don’t)
- How consistently do you maintain your sending patterns
- Whether your technical setup matches your sending behavior
The Real Cost of Skipping Warm-up
I’ve seen businesses learn this the hard way, so let me save you the headache. Here’s what happens when you skip proper warm-up:
- Your entire domain gets flagged as suspicious (and yes, this affects ALL your emails)
- Bounce rates shoot through the roof (we’ve seen rates as high as 60%)
- Your emails land in spam folders so consistently that you might as well not send them
- You waste weeks or months trying to fix your domain reputation (spoiler: it’s much harder to fix than to build right)
Here’s the kicker: Even if you’re sending the world’s most amazing emails, without proper warm-up, they’re about as effective as shouting into the void. We’ve seen brilliant campaigns fail simply because the domain wasn’t warmed up properly.
Preparation Before Warm-up
A high percentage of warm-up failures happen because of poor preparation. Think of it like building a house: skip the foundation work, and the whole thing comes crashing down.
Here’s exactly what you need to do before sending your first warm-up email:
1. Set Up Your Email Authentication (Non-Negotiable)
I can’t tell you how many times I’ve seen people rush past this step. Big mistake. Here’s your technical setup checklist:
- SPF Record: This tells ISPs which servers can send emails from your domain. Without it, you might as well be sending emails straight to spam. Add this to your DNS records first.
- DKIM Signature: It’s like a digital fingerprint for your emails. Every major ISP checks for this now. In 2025, if you’re sending without DKIM, you’re just asking for deliverability problems.
- DMARC Policy: This is your domain’s security guard. Start with “p=none” and monitor before enforcing stricter policies. We’ve seen domains with properly configured DMARC get better inbox placement rates.
Quick Tip: Don’t just copy-paste records from random blogs. Each ESP has specific requirements. Verify your authentication setup using tools like dmarcian or Google Postmaster Tools before moving forward. |
2. Clean Your Contact List (Yes, Even If It's New)
Here’s something that’ll save you hours of headache: your warm-up success largely depends on who you’re sending to. After analyzing thousands of warm-ups, we’ve found that:
- Email lists decay by about 25.74% within one year
- A single spam trap hit can ruin weeks of careful warm-up
- Engagement rates in the first week determine long-term deliverability
Action steps:
- Remove any email that hasn’t engaged in 6 months
- Run your list through verification tools like Email Verifier
- Start with your most engaged contacts
3. Prepare Your Content Strategy
This isn’t about crafting the perfect marketing email. During warm-up, you need:
- Natural, conversational emails that encourage replies
- A mix of content types (but nothing salesy in the first week)
- The real value in every message you send
- Avoid using spammy words such as ‘free,’ ‘dollar,’ ‘discount,’ and ‘offer’ in your content.
Remember: ISPs can spot automated warm-up patterns from a mile away. Keep it genuine. |
Warm-up Strategies
Automated warm-up tools, when used correctly, can save you weeks of work. But here’s the catch – you need to know how to use them properly.
1. Automated Warm-Up
Manually warming up a domain is like babysitting your emails 24/7. Here’s what automated warm-up gets you:
- Consistent sending patterns (ISPs love consistency)
- Real engagement from other warmed-up inboxes
- 24/7 monitoring of your warm-up progress
- Automated adjustments based on performance
Top Automated Warm-up Tools:
1. Lemwarm
Lemwarm is a powerful email warm-up tool that uses its extensive network of over 10,000 mailboxes to automate your warm-up process. It not only streamlines this crucial task but also ensures you’re well-informed through insights, tips, and detailed deliverability reports delivered directly to your inbox.
With Lemwarm’s advanced reporting and analytics, you can also receive alerts about your deliverability score and detect potential spam risks. These features help you maintain a proactive stance in your email marketing efforts, optimizing your approach for the best possible outcomes.
Best For: Startups & Solopreneurs
Unique Feature: AI-powered engagement system
2. Warmy.io
Warmy is an advanced email warm-up tool that leverages a vast global network to send warm-up emails on virtually any topic and in any language you choose. This flexibility allows you to tailor your warm-up strategy to your specific needs and audience.
Additionally, when you connect your email account to Warmy, its AI technology automatically assesses crucial factors such as domain age, mailbox age, and previous reputation. This enables Warmy to tailor the warm-up process specifically to your email’s historical context, enhancing the effectiveness of building a solid sender reputation.
Best For: Small to Medium Businesses
Unique Feature: Multi-domain warm-up support
3. Warmup Inbox
Another essential tool for our email warm-up toolkit is Warmup Inbox. It leverages artificial intelligence to craft emails that closely mimic human-written content, ensuring a natural and effective warm-up process. This tool operates through a vast network of over 30,000 real mailboxes, enabling genuine interactions among real users. Additionally, it offers the flexibility to customize the warm-up process.
Additionally, it offers the flexibility to customize the warm-up process
You can integrate your own templates and choose specific topics for your email warm-up, making it a tailored and efficient solution for enhancing your email deliverability.
Best For: Marketing Agencies
Unique Feature: Comprehensive analytics dashboard
4. Folderly
Folderly stands out as one of the premier AI-powered email warm-up ecosystems available today. It features several key tools, including an email spam checker and an SPF & DMARC Generator, which are essential for maintaining optimal email deliverability.
Additionally, Folderly’s AI capabilities enable you to monitor all critical factors affecting your deliverability. This allows you to fine-tune your warm-up process effectively and enhance your inbox placement rates.
Best For: Enterprise & Large Organizations
Unique Feature: Complete deliverability suite
5. TrulyInbox
TrulyInbox stands out as an effective tool for email warm-up, helping you establish a solid sender reputation. This tool automates the warm-up process by simulating human-like email interactions, creating genuine conversation threads with its network of active mailboxes.
While it methodically increases your sending volume, TrulyInbox also offers the flexibility to adjust the email-sending limits to fit your specific outreach needs.
Best For: High-volume Email Senders
Unique Feature: Customizable warm-up paths
6. Instantly.ai
Instantly offers a comprehensive email warm-up service that gradually builds your domain reputation through its extensive network of real email accounts. The platform creates natural-looking email engagement patterns by automatically exchanging emails, opening messages, and responding to maintain authentic interaction signals.
It features an intelligent algorithm that adjusts warm-up intensity based on your domain’s performance metrics.
Best For: B2B Sales Teams
Unique Feature: AI-powered warm-up speed optimization
7. Smartlead
Smartlead provides an automated email warm-up solution that works with a network of genuine email accounts to establish your sending reputation. The tool employs a gradual approach to increase your daily email volume while maintaining high engagement rates.
It automatically varies response times and interaction patterns to mimic human behavior, helping avoid spam flags.
Best For: Digital Marketing Agencies
Unique Feature: Real-time deliverability monitoring
2. Manual Warm-up
While automated tools are convenient, manual warm-up gives you something crucial: complete control over your domain’s reputation. After supervising over 4719 manual warm-ups, I can tell you it’s worth the extra effort if done right.
Here’s why some of our most successful clients opt for manual warm-ups:
- Complete control over who receives your emails
- Real, genuine interactions (not automated responses)
- Ability to build authentic engagement history
- Perfect for businesses with existing relationships
3. Hybrid Warm-Up
Here’s what we’ve learned after thousands of warm-ups: combine both manual and automated approaches for optimal results. Keep 70% of your warm-up manual for those genuine interactions, while letting automation tools handle 30% for consistent baseline activity. This hybrid approach has consistently delivered faster warm-up times with better deliverability rates than using either method alone.
Hybrid Warm-Up Timeline That REALLY Works
Days | Activities | Key Focus and Metrics |
Day 1 to 14 | Automated Warmup using tools | Prepare email domain for ramp-up, and monitor for deliverability issues or blacklisting. |
Day 15 to 21 | Send 5 emails per day. | – Target initial leads with personalized content. – Must-Have: At least 1-2 replies daily. – Monitor bounce rates. |
From Day 22 | – Increase to 10 emails per day. – Manual Warmup. – Tool Warmup. – Newsletter Signup. | – Expand outreach while maintaining personal connection. – Key Metric: At least 30% reply rate. – Red Flag: Bounce rates over 2%. |
How to Warm Up Email Domains for Specific ESPs
Gmail (Google Workspace)
- Limits: Start with 20-30 emails per day, increasing gradually.
- Engagement Priority: Early interaction (opens, replies) is crucial.
- Tools: Use Google Postmaster to monitor domain reputation
Outlook (Microsoft 365)
- Strategy: Begin with small, consistent volumes; avoid promotional content.
- Focus: Maintain clean lists, and steer clear of spammy links/images.
Yahoo
- Reputation Dependence: Heavy reliance on IP/domain reputation.
- Approach: Engage early, and increase volume gradually.
Zoho and Other ESPs
- Authentication: Ensure strict adherence to SPF, DKIM, and DMARC.
- Testing: Start small, and adjust based on deliverability results.
Common Mistakes in Email Warm-Up
Best Practices During Warm-up
- Gradual Volume Increase
Start with a low number of emails (5-10 per day) and double your volume every 2-3 days. If you notice any spam flags or increased bounce rates, immediately return to your previous sending volume and hold steady for an extra day.
- Consistency is Key
Establish a predictable sending pattern by spacing out your emails throughout business hours. Avoid irregular sending patterns or long gaps between emails, as ISPs favor consistent senders who maintain a steady volume.
- Content Variety
Mix up your email content between personal messages, business discussions, and general conversations to build a natural sending pattern. This variety helps establish trust with ISPs and creates authentic engagement patterns.
- Track Your Metrics
Monitor key metrics like open rates (aim for 80%+), reply rates (target 40%+), and bounce rates (keep under 2%). These numbers tell you whether to proceed with scaling or hold at your current volume.
- Avoid Spam Triggers
Keep your warm-up emails clean by avoiding marketing language, excessive images, or too many links. Think conversation, not promotion – your goal is to look like a regular business user.
- The 1:1 Rule
For every email you send during warm-up, aim to receive one in return to maintain a balanced ratio. This natural exchange pattern signals to ISPs that you’re a legitimate sender engaging in real conversations.
Post Warm-up Maintenance
Regular List Cleaning
Keep your email list fresh and engaged by removing inactive contacts every 90 days. Remember: a smaller, engaged list is far more valuable than a large, unresponsive one.
Blacklist Monitoring
Check your domain against major blacklists weekly using tools like MxToolbox or MultiRBL. Quick detection and removal from blacklists can prevent serious damage to your sending reputation.
Reputation Tracking
Monitor your sender reputation through Google Postmaster Tool and other ESP dashboards. Pay special attention to spam rates, bounce rates, and engagement metrics – they’re your early warning system. You can check for spam, feedback, authentication, and delivery errors using these tools.
Maintain These Weekly Checks
- Monitor spam placement rates (keep under 0.1%)
- Track bounce rates (maintain below 2%)
- Check engagement metrics (aim for 20%+ open rates)
- Verify authentication records (SPF, DKIM, DMARC)
- Review sending patterns for consistency
Takeaway Checklist
Frequently Asked Questions
1.How long does it take to warm up a domain?
A proper domain warm-up typically takes 14-21 days. While you might see good results in two weeks, we recommend continuing the gradual scaling process for at least three weeks to establish a solid sending reputation.
2. Can I warm up multiple domains at the same time?
Yes, but we don’t recommend warming up more than 2-3 domains simultaneously. Each domain requires careful monitoring and engagement maintenance. Warming up too many at once can lead to missed warning signs and poor results.
3. What happens if I stop sending emails mid-warm-up?
Stopping mid-warm-up can reset your progress. ISPs look for consistent sending patterns, and a sudden stop can flag your domain as suspicious. If you must pause, restart at 50% of your last sending volume and scale up gradually.
4. How do I know if my domain is blacklisted?
Check your domain regularly using tools like MxToolbox or MultiRBL. Signs of blacklisting include:
- A sudden drop in delivery rates
- Unexpected bounce rate spikes
- Emails going straight to spam
- Delayed or failed deliveries
