Whether you're launching a cold outreach campaign, onboarding a new domain, or switching email platforms, email warm-up is the critical first step in achieving high inbox placement.
This post breaks down everything you need to know about warming up your email infrastructure and scaling cold outreach without burning your sender reputation.
What is email warm-up?
Email warm-up is the process of gradually increasing the volume of emails sent from a new or inactive mailbox/domain while generating engagement (opens, replies). Warmup is not limited to only sending emails but also receiving emails. It signals ESPs like Gmail, Outlook, and Yahoo that: “This is a real sender people engage with, not a spammer.”
How warmup tools simulate warmup:
Because warm-up tools continue to send their own internal emails (simulating engagement), and if you suddenly add 40 cold emails/day on top of that, your total daily sending volume doubles to 80, a sudden spike that Gmail or Outlook might flag as suspicious.
As a rule of thumb:
Choose a cold outreach platform with:
This post breaks down everything you need to know about warming up your email infrastructure and scaling cold outreach without burning your sender reputation.
What is email warm-up?
Email warm-up is the process of gradually increasing the volume of emails sent from a new or inactive mailbox/domain while generating engagement (opens, replies). Warmup is not limited to only sending emails but also receiving emails. It signals ESPs like Gmail, Outlook, and Yahoo that: “This is a real sender people engage with, not a spammer.”
How warmup tools simulate warmup:
- These tools simulate email sending with opens and replies
- If any emails land in spam, they move to the inbox and mark it as important
- Tweaks/randomize the content for every email, replicating real conversations
- Gradually increases the email sending over the days
- TrulyInbox
- Warmy
- Mailreach
- Lemwarm (Lemlist)
- Warmup Inbox
- Send daily human-like messages to different inboxes.
- Use randomized content for each email.
- Monitor where emails are landing, remove them from spam if they are landing their
- Adjust the volume accordingly when spam hit ratio is high
- Maintain at least 25-30% response/reply rate
- Cold starts trigger email filters: Domains that go from 0 → 100 emails/day get flagged fast.
- Spam filters use ML: Especially Gmail, which builds recipient-specific models and analyzes the overall activity.
- Reputation: It resets after inactivity, even for older domains.
- Domain Authentication:
- SPF
- DKIM
- DMARC
- Use tools to test the configuration: MXToolbox or Google Admin Toolbox
- Gmail Postmaster Tools
- If you are sending emails to Gsuite users, register your domain at https://postmaster.google.com.it gives you insights into how Gmail perceives your domain and sending behavior.
- Domain Age Check:
- Brand new domains need extra caution. Ideally, wait 7–14 days after registration before warming
- Avoid links, images, attachments
- Use unique text (no templates)
- Encourage replies (they’re gold!)
- Warm up for at least 2–4 weeks
- Keep warm-up running even after deliverability is stable
- Start Cold Email in Small Batches:
- Start small and increase gradually according to your warmup volume
- Monitor deliverability, open & reply rates, and adjust the volume if necessary.
- Avoid large spikes, even if the domain is warm
Because warm-up tools continue to send their own internal emails (simulating engagement), and if you suddenly add 40 cold emails/day on top of that, your total daily sending volume doubles to 80, a sudden spike that Gmail or Outlook might flag as suspicious.
As a rule of thumb:
- Start cold outreach at 25–40% of the warmed-up volume
- Scale slowly (10–15% every few days)
- Don’t exceed 2–3x the warm-up volume in total without warm-up continuing in parallel.
Choose a cold outreach platform with:
- Per-mailbox sending limits
- Sending windows (e.g., 9am–5pm)
- Spintax/randomization
- Inbox rotation
- Email throttling feature (time between each email)
- Recommended: Instantly, Smartlead, Saleshandy, Woodpecker
- Gmail/Google Workspace: 150–200
- Outlook/Microsoft Office: 100–150
- Zoho Mail: 100–150
- Gmail Postmaster Tools(https://postmaster.google.com/)
- Cisco Talos Intelligence(https://talosintelligence.com)
- MXToolbox Blacklist Checker(https://mxtoolbox.com/blacklists.aspx)
- SNDS for Outlook(https://sendersupport.olc.protection.outlook.com/snds/)
- Continue background warm-up (10–20/day)
- Focus on human-like, value-first content
- Never reuse the same subject/body across 100s of leads
- Rotate inboxes if scaling to 1000s/day
- Keep monitoring reputation even post warm-up