A new domain has zero sender reputation. Sending 100 cold emails on day one trips every spam filter at Gmail, Outlook, and Yahoo, your domain ends up on blocklists within 48 hours, and recovery takes weeks.

This is part of our Complete Guide to Cold Email Deliverability — the four pillars that decide inbox placement.

Warmup is the process of building sender reputation gradually so by the time you're sending real cold email volume, receivers trust you. Done right, it takes 14 days of measured ramp before you can send your first real campaign.

What "reputation" actually means

Receivers track three signals per domain:

Engagement rate, opens, replies, stars, forwards
Complaint rate, recipients clicking "Report Spam"
Volume velocity, how fast your daily volume is changing

A trusted domain has high engagement, near-zero complaints, and gradual volume changes. Warmup mimics that profile artificially before you have real recipients.

The 14-day plan

Day	Sends/day	Targets	Engagement
1	5	100% peer pool	Reply rate 80%+
2	8	100% peer pool	Reply rate 80%+
3	12	100% peer pool	Reply rate 70%+
4	18	80% peer / 20% real	Reply rate 70%+
5	25	70% peer / 30% real	Reply rate 60%+
6	35	60% peer / 40% real	Reply rate 60%+
7	50	50% peer / 50% real	Reply rate 50%+
8	65	40% peer / 60% real	Reply rate 50%+
9	80	30% peer / 70% real	Reply rate 40%+
10	100	20% peer / 80% real	Reply rate 40%+
11	120	10% peer / 90% real	Reply rate 30%+
12	140	100% real	Reply rate 30%+
13	150	100% real	Reply rate ~real
14	150	100% real	Reply rate ~real

After day 14, hold steady at 150/day, the practical ceiling for a single Workspace mailbox. Don't push further unless you've been at that volume for 30 days with no deliverability degradation.

What "peer pool" means

A peer pool is a set of mailboxes that automatically reply to your warmup emails (and you reply to theirs). The reply, archive, and star/flag actions tell Google "this domain sends mail people want."

Critical: peer-pool mail must look real. The signals receivers value:

✅ Replies (especially within 24 hours)
✅ Mail moved out of spam folder back to inbox
✅ Sender added to contacts
✅ Email forwarded to another address
✅ Mail starred / labeled
❌ Bulk mark-as-read (looks botted)
❌ Identical reply text across all peers (filters detect this)

Tools that randomize reply text + timing produce realistic patterns. Tools that don't get caught and actually hurt reputation.

Mistakes that ruin warmup

Skipping warmup entirely. Sending 50 cold emails on day 1 from a new domain is a one-way ticket to a spam-folder placement that takes 4-6 weeks to recover from.

Ramping too fast. Doubling daily volume in one day (e.g. day 6 → 80/day instead of the planned 35) reads as a botnet to Google's classifier.

Mixing warmup and real campaigns too early. Real cold email recipients have low reply rates (1-5%). Mixing them in before day 7 crashes your apparent engagement rate.

Not signing email properly. No DKIM = warmup is wasted. Set up DKIM before day 1, see the DKIM setup guide.

After warmup: maintenance

Reputation is a flywheel, if you stop sending, it decays. To stay warm:

Send at least 30 mail/day, every day, including weekends
Maintain reply rate above 5% on real campaigns
Keep bounce rate below 5% (verify lists with NeverBounce / ZeroBounce)
Watch Google Postmaster Tools for reputation drops

Doing it manually vs. using a tool

You can run a 14-day warmup manually, set up a personal "test" mailbox, exchange canned replies with it, gradually send to real contacts. Most people don't have the patience and break the schedule on day 4.

Bulk Email Boxer's warmup runs on autopilot, you connect a mailbox, flip the switch, and our peer pool handles the back-and-forth with randomized timing and natural-looking reply text. The dispatcher respects per-day caps automatically. Start your free 14-day trial to get on the rollout.

Once warmup completes, the next thing to monitor is your day-to-day deliverability checklist. The two together get you from cold-domain to inbox-reliable in under three weeks.