Email warmup means building a new domain’s or inbox’s sending reputation slowly, so Gmail and Outlook learn to trust it before you send at volume. Done properly, it takes 2 to 4 weeks. Set up SPF, DKIM and DMARC, start with 10 to 20 emails a day to people likely to reply, and increase gradually while your spam complaint rate stays under 0.1%. Google’s own sender guidelines say the same thing in plainer words: start with low volume to engaged users and increase slowly. Warmup tools automate part of this by exchanging emails with a network of inboxes. They help, but they don’t fix a bad list or a spammy message.
Key Takeaways
- Authentication is now mandatory. Gmail requires SPF or DKIM from every sender, and SPF, DKIM, DMARC and one-click unsubscribe from anyone sending 5,000 or more emails a day. Outlook has bounced non-compliant mail from senders over 5,000 a day since 5 May 2025.
- The spam complaint line is 0.3%. Gmail asks senders to stay below 0.1% and never reach 0.3%.
- Gmail has been enforcing harder since November 2025, with temporary rate limits and permanent rejections for non-compliant mail.
- Warmup tools cost $15 to $49 per inbox a month, or come bundled with outreach tools. Instantly includes unlimited warmup from $37.60 a month on annual billing.
- Warmup reports can flatter you. One warmup vendor found its Gmail inbox rate was about 10 points lower when measured through Gmail’s own tabs (OAuth) than through standard IMAP folder checks.
Who Needs Email Warmup
| Situation | Warmup needed? |
|---|---|
| New domain bought for cold outreach | Yes, 3 to 4 weeks before any campaign |
| New Google Workspace or Microsoft 365 inbox on an existing domain | Yes, 2 to 3 weeks |
| Existing inbox jumping from 20 to 200 emails a day | Yes, ramp gradually |
| Newsletter to people who signed up | Ramp volume, but a warmup network isn’t needed |
| Normal one-to-one business email | No |
| Inbox already landing in spam | Pause campaigns, fix the cause, then warm up again |
Step 1: Set Up the Domain Before Sending Anything
Most outreach teams use a separate domain for cold email, such as getyourbrand.com alongside yourbrand.com, so a reputation problem can’t affect your main company email.
Add these DNS records with your domain provider. Replace the placeholders with your own values:
text
# SPF: lists who may send for your domain (Google Workspace example)
yourdomain.com. TXT "v=spf1 include:_spf.google.com ~all"
# DKIM: generate the key in Google Workspace or Microsoft 365 admin, then publish it
google._domainkey.yourdomain.com. TXT "v=DKIM1; k=rsa; p=YOUR-PUBLIC-KEY"
# DMARC: start with monitoring only
_dmarc.yourdomain.com. TXT "v=DMARC1; p=none; rua=mailto:dmarc@yourdomain.com"Then:
- Point the outreach domain’s website to your main site, so a visitor who checks it finds a real business.
- Add a profile photo and signature to each inbox.
- Register the domain in Google Postmaster Tools to watch your spam rate once volume grows.
- Send a test to a Gmail account and check “Show original”: SPF, DKIM and DMARC should all say PASS.
Step 2: Follow a Gradual Sending Schedule
This is a conservative starting schedule for one new inbox. Count only real emails, not warmup-tool traffic.
| Week | Real emails per day | Who to send to |
|---|---|---|
| 1 | 5 to 10 | Colleagues, partners and existing contacts who’ll reply |
| 2 | 15 to 25 | Warm leads and past customers |
| 3 | 30 to 40 | Mix of warm and well-targeted cold prospects |
| 4 | 40 to 50 | Cold prospects, if spam rate stays below 0.1% |
| After week 4 | Up to 50 per inbox | Add inboxes instead of pushing one inbox higher |
Google’s free Gmail accounts are capped at 500 messages a day and Google Workspace accounts at 2,000, but those are limits, not targets. Many outreach teams cap each inbox at about 30 to 50 cold emails a day and spread volume across several inboxes and domains.
If a warmup tool is running, it adds its own emails on top. Most start at 5 to 10 a day and ramp to 30 to 40, and you can usually leave it running at a low level after the warmup period.
Step 3: Meet Gmail and Outlook’s Sender Rules
| Requirement | Gmail (all senders) | Gmail (5,000+/day) | Outlook (5,000+/day) |
|---|---|---|---|
| SPF or DKIM | Required | Both required | Both required |
| DMARC | Recommended | Required (p=none is enough) | Required (p=none is enough) |
| From domain aligned with SPF or DKIM | Recommended | Required | Required |
| One-click unsubscribe | Recommended | Required for marketing mail | Recommended |
| Spam complaint rate | Below 0.3% | Below 0.3%, aim for 0.1% | Low complaint rate expected |
| What happens if you don’t comply | Delays and spam folder | Rate limits, then rejections | Bounced with error 550 5.7.15 |
Gmail’s 5,000-a-day classification is permanent once you’ve reached it, even if your volume later drops. Since November 2025, Gmail has been gradually enforcing the rules with temporary errors, then permanent rejections, for non-compliant traffic.
Step 4: Decide Whether You Need a Warmup Tool
A warmup tool connects your inbox to a network of other inboxes that send emails to each other, open them, reply and move them out of spam. That creates positive signals while your real volume is still low.
| Tool | Price | Pricing model |
|---|---|---|
| Instantly | From $37.60/mo (annual) or $47 monthly | Unlimited inboxes and warmup with outreach plan |
| lemwarm | $24/inbox/mo annual ($29 monthly) | Per inbox; free with lemlist paid seats |
| MailReach | From about $20 to $25 per inbox/mo | Per inbox, with placement tests |
| Warmup Inbox | From about $15/inbox/mo (annual) | Per inbox |
| Warmy | About $49/inbox/mo | Per inbox, demo for tiers |
| Mailivery | From $29/mo or $21.75/mo (annual) for unlimited inboxes | Flat |
Gmail and Outlook sender rules and warmup tool prices change often, so check current requirements before you start. For AI-led outreach tools that sit on top of these inboxes, see our AI SDR tools comparison.
What Warmup Tools Can and Can’t Do
Warmup Inbox analysed about 17,000 inboxes on its own network (May 2026 data). Median inbox placement rose from 95.2% in week one to 98.8% after 12 weeks, and the spam rate fell from 1.8% to 0.2%. The same study found two caveats worth knowing:
- Measured through Gmail’s API, which sees the Primary and Promotions tabs, Gmail placement was about 10 points lower than through standard IMAP folder checks. A warmup dashboard can look better than reality.
- When placement dropped and was fixed within 3 days, it recovered in 7 to 9 days. Drops left for over 15 days took 57 to 74 days, and only about half fully recovered.
That’s vendor data from the vendor’s own customers, but it matches what deliverability specialists usually say: warmup shortens the ramp, while list quality and message content decide whether you stay in the inbox.
Step 5: Protect Your Reputation Once You’re Sending
- Verify every list before sending and keep bounces under 2%.
- Send plain-text style emails with one link at most in the first message.
- Personalise the first line, and avoid identical messages to hundreds of people.
- Stop sequences as soon as someone replies or asks to be removed.
- Add an easy opt-out line to cold emails.
- Check Postmaster Tools and your warmup tool’s placement tests weekly.
- Pause a domain the day its spam rate goes over 0.1%.
Common Email Warmup Mistakes
- Sending a full campaign in the first week.
- Running cold email from your main company domain.
- Skipping DMARC because “p=none doesn’t do anything.”
- Trusting warmup dashboard scores without a real placement test.
- Buying lists and hoping warmup will cover the bounces.
- Turning warmup off the moment the campaign starts.
Tools for Newsletters and Transactional Email
Warmup networks are for one-to-one outreach inboxes. For newsletters and product email, your email platform handles reputation on its own sending infrastructure. Ramp volume to your most engaged subscribers first. Our Brevo profile covers its plans, and Mailmeteor is a simpler option for personalised Gmail mail merges at low volume.
