How to Warm Up Email Accounts for Cold Email (Step-by-Step 2026)

Email warmup is the process of gradually building sending reputation for a new domain or mailbox before using it for cold outreach. Skip it and your emails go straight to spam — or get the domain blocked entirely.

Why Warmup Is Necessary

Inbox providers like Gmail and Outlook maintain a reputation score for every sending domain and IP address. A brand-new domain that sends 500 cold emails on day one has no track record — which triggers spam filters by default.

Warmup establishes that history artificially: automated tools send emails between a network of real mailboxes that are then opened, replied to, and un-spammed. This pattern — sending, opening, replying — builds positive reputation signals before you introduce cold recipients.

The #1 mistake: Starting cold outreach before warmup is complete. Three weeks minimum for a new domain. There are no shortcuts — domain reputation is time-weighted.

Warmup Timeline

Week	Warmup volume/day	Cold email volume/day	Focus
Week 1	10–20	0	Foundation — DNS, authentication, warmup only
Week 2	20–40	0	Monitor Gmail Postmaster, verify domain health
Week 3	40–60	20–30	Introduce cold email at very low volume
Week 4	60–80	50–70	Ramp cold email 20–30% every 3 days
Month 2+	Ongoing	Up to 50/mailbox/day	Normal operations — keep warmup running

What Warmup Tools Actually Do

Warmup tools like those built into Smartlead and Instantly work by connecting your mailbox to a network of seed accounts. These seed accounts:

Receive your warmup emails and open them
Reply to a percentage of them (reply signals are weighted heavily)
Move them out of spam if they land there
Mark them as "not spam" and "important"

The result is a stream of positive engagement signals flowing into Gmail and Outlook's reputation algorithms — all from your sending domain.

Keep warmup on permanently. Even at full sending capacity, keep warmup running at 30–50 emails/day. The buffer of positive engagement offsets complaint signals from cold email. Turning warmup off is like removing a safety net.

Domain Setup Before Warmup

Before starting warmup, your DNS must be fully configured:

SPF record — authorizes your mail server to send from the domain
DKIM record — cryptographic signature (2048-bit key, required by Gmail since 2024)
DMARC record — minimum p=none with reporting email
MX records — even if you're not receiving email, MX records should exist
Custom tracking subdomain — avoids reputation spillover from shared ESP tracking domains

See the full deliverability guide for step-by-step DNS configuration.

Warmup Included vs Paid Add-On

Tool	Warmup included?	Network size	Cost
Smartlead	✓ Unlimited, all plans	Large proprietary network	Free with plan
Instantly	✓ Unlimited, all plans	Large proprietary network	Free with plan
Lemlist	✓ Included	Moderate network	Free with plan
Mailwarm (standalone)	Warmup only	5,000+ seed accounts	$69+/mo
Warmy.io (standalone)	Warmup only	50,000+ seed accounts	$49+/mo

Signs Your Warmup Isn't Working

Gmail Postmaster shows "Low" or "Bad" domain reputation after 3 weeks
Bounce rate above 3% on warmup emails (usually means DNS is misconfigured)
Emails landing in spam during warmup itself
No open activity on warmup emails (check that your warmup tool is connected properly)

Common Questions

Minimum 3 weeks before any cold outreach. 4 weeks is safer. New domains registered in the last 30 days should be treated as high-risk — take the full 4 weeks and start at lower volumes.

Yes — and you should. Smartlead and Instantly warm up unlimited mailboxes simultaneously on all plans. Run warmup on all your mailboxes in parallel from day one of domain setup.

Yes. Keep warmup running permanently at a lower volume (20–40/day). It provides a continuous buffer of positive engagement signals that counterbalances any complaint signals from cold email recipients.

Written by

Scott Holmes

Cold email infrastructure specialist. Founder of Pinnacle Tech Projects.

How to Warm Up Cold Email Accounts (Step-by-Step)

Why Warmup Is Necessary

Warmup Timeline

What Warmup Tools Actually Do

Domain Setup Before Warmup

Warmup Included vs Paid Add-On

Signs Your Warmup Isn't Working

Common Questions