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general email-warmup-strategy

email-warmup-strategy

This skill should be used when the user asks to "warm up an email domain", "set up email warmup", "warm up a sending inbox", "design an email warmup plan", "warm up a new domain for cold email", "prepare a domain for outbound", "how long to warm up an email", "warm up strategy for cold outbound", "set up domain warmup before sending", or any variation of warming up new or existing email domains and inboxes for B2B SaaS cold outbound.

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Email Warmup Strategy

Email warmup is the process of gradually building sending reputation on a new domain or inbox by starting with low-volume, high-engagement email and slowly increasing volume over 2-4 weeks. A new domain with no sending history that blasts 200 cold emails on Day 1 will land in spam. A domain that sends 5 emails on Day 1, 10 on Day 5, 20 on Day 10, and 50 on Day 20 builds a reputation as a legitimate sender.

The principle: mail providers (Google, Microsoft, Yahoo) judge your domain's reputation based on sending patterns, engagement rates, and complaint rates. Warmup teaches these providers that your domain sends legitimate email that recipients want. Skip warmup and you teach them the opposite.

When Warmup Is Required

Scenario	Warmup needed?	Duration
Brand new domain (just registered)	Yes, mandatory	3-4 weeks minimum
New subdomain on existing domain	Yes	2-3 weeks
New inbox on existing warmed domain	Yes (lighter)	1-2 weeks
Existing domain, no cold email history	Yes	2-3 weeks
Existing domain, paused cold email for 60+ days	Yes (re-warmup)	1-2 weeks
Existing domain, sending consistently	No	Maintain sending volume. Don't spike
Switched email provider (Google → Microsoft)	Partial	1 week. The domain has history but the IP is new

The 4-Week Warmup Plan

Week-by-week volume ramp

Day	Emails per day	Type of email	Engagement target
1-3	5-10	Manual 1:1 email to known contacts (colleagues, partners, friends)	100% open, 50%+ reply
4-7	10-20	Manual 1:1 + warmup tool (automated warmup network)	80%+ open, 30%+ reply
8-14	20-40	Warmup tool + small cold batches (5-10 cold per day)	60%+ open, 20%+ reply (warmup), monitor cold metrics
15-21	40-60	Warmup tool continues + increase cold to 20-30 per day	Monitor bounce rate (< 3%), spam complaints (< 0.1%)
22-28	50-80	Reduce warmup to maintenance level. Cold at target volume (30-50/day)	Stable inbox placement. Bounce < 3%. No spam spikes
29+	Target volume (30-50/day)	Warmup tool at maintenance (5-10/day). Cold at full volume	Ongoing monitoring

Volume ramp rules

Never more than 2x increase from one week to the next. Going from 10/day to 50/day in one week is too fast. Go 10 → 20 → 40 → target
Include warmup volume alongside cold volume. Don't replace warmup with cold. Run both in parallel during weeks 2-4. Warmup provides positive engagement signals that offset cold email's lower engagement
Daily send limit per inbox: 50 max for cold email. Even after warmup, don't send more than 50 cold emails per day from a single inbox. Use inbox rotation for higher volume (see inbox-rotation skill)
Weekdays only. Don't send warmup or cold email on weekends. B2B email is a weekday activity. Weekend sends look like spam bots

What counts as warmup email

Type	How it works	Engagement quality
Manual 1:1 to known contacts	Email colleagues, partners, vendors. Real conversations	Highest. Real replies, real opens
Newsletter subscriptions	Subscribe the inbox to 10-15 industry newsletters. Open and click	Medium. Opens signal engagement to mail providers
Warmup tool (automated)	Service sends emails between accounts in a warmup network. Auto-opens, auto-replies, auto-removes from spam	Medium-high. Simulates real engagement at scale
Reply to inbound	Reply to any email the inbox receives. Newsletters, notifications, etc.	High. Real replies on real threads

Warmup email rules:

Manual 1:1 is the highest-quality warmup. Real conversations with real people. Mail providers reward this
Warmup tools are the most scalable. They run in the background and generate engagement signals automatically. Use them for 80% of warmup volume
Never use warmup-only email (no real sending at all). The pattern of only sending to warmup networks looks artificial. Mix real email (cold or manual) with warmup from Day 1

Warmup Tools

Major warmup tools

Tool	How it works	Cost	Integrated with
Lemwarm (Lemlist)	Warmup network of Lemlist users. Auto-sends, opens, replies, removes from spam	Included with Lemlist paid plans	Lemlist
Mailwarm	Standalone warmup. Network of real inboxes	$69-159/month per inbox	Any email provider
Warmup Inbox	Standalone. Network-based warmup	$9-99/month per inbox	Any email provider
Instantly Warmup	Warmup network for Instantly users	Included with Instantly plans	Instantly
Smartlead Warmup	Warmup for Smartlead users	Included with Smartlead plans	Smartlead
Apollo Warmup	Basic warmup within Apollo	Included on some plans	Apollo

Tool selection

Your situation	Best tool	Why
Already using Lemlist	Lemwarm	Included in plan. Integrated with sequencing
Already using Instantly	Instantly Warmup	Included. Tight integration
Already using Smartlead	Smartlead Warmup	Included. Native
Using Outreach or Salesloft (no native warmup)	Mailwarm or Warmup Inbox	Standalone tools that work with any provider
Budget-conscious, standalone	Warmup Inbox	Lowest cost standalone option

Warmup tool rules

Keep warmup running forever, not just during the initial ramp. After the 4-week ramp, reduce to maintenance level (5-10 warmup emails per day). This maintains the positive engagement signals that keep your reputation healthy
Monitor warmup dashboard daily during weeks 1-2. Most tools show inbox placement rate (what % of warmup emails land in inbox vs spam). Target > 95% inbox placement before starting cold sends
If inbox placement drops below 80% during warmup: Stop cold sending. Continue warmup-only for 1 week. Check SPF/DKIM/DMARC. Check for blacklisting. Don't resume cold until placement recovers to > 90%

Warmup by Domain Type

New domain (just registered)

Step	Timing	Action
1	Day 0	Register domain. Set up Google Workspace or Microsoft 365. Configure SPF, DKIM, DMARC
2	Day 1-3	Send manual 1:1 emails only. 5-10/day. Real conversations
3	Day 1	Activate warmup tool. Start at 5-10 warmup emails/day
4	Day 4-7	Increase warmup to 15-20/day. Continue manual emails
5	Day 8-14	Warmup at 20-30/day. Start cold at 5-10/day
6	Day 15-21	Warmup at 20-30/day. Cold at 15-25/day
7	Day 22-28	Warmup at 10-15/day (maintenance). Cold at 30-50/day
8	Day 29+	Warmup at 5-10/day (permanent maintenance). Cold at target volume

New domain minimum warmup: 3-4 weeks. Don't rush this. A new domain has zero reputation. Building from zero takes time.

New subdomain on existing domain

Step	Timing	Action
1	Day 0	Create subdomain. Set up SPF, DKIM, DMARC for subdomain
2	Day 1-3	Manual 1:1 + warmup tool at 10-15/day
3	Day 4-10	Warmup at 20-25/day. Start cold at 10-15/day
4	Day 11-21	Warmup at 15-20/day. Cold at 25-40/day
5	Day 22+	Warmup at 5-10/day. Cold at target volume

Subdomain warmup: 2-3 weeks. The parent domain's reputation provides a slight head start, but the subdomain still needs its own sending history.

Existing inbox re-warmup (paused 60+ days)

Step	Timing	Action
1	Day 0	Activate warmup tool at 10-15/day
2	Day 1-5	Warmup only. No cold sending
3	Day 6-10	Warmup at 15-20/day. Cold at 10-15/day
4	Day 11+	Warmup at maintenance. Cold at target volume

Re-warmup: 1-2 weeks. The domain has history but reputation decays during inactivity. A shorter ramp is sufficient.

Monitoring During Warmup

Daily checks (weeks 1-2)

Check	Where	Target	Red flag
Inbox placement rate	Warmup tool dashboard	> 95%	< 80%
Bounce rate on cold sends	Sequencing tool	< 2%	> 3%
Spam complaint rate	Email provider admin	< 0.1%	> 0.3%
Blacklist status	MXToolbox Blacklist Check	Not listed	Any listing
SPF/DKIM pass rate	Email headers on test sends	100% pass	Any failure

Weekly checks (weeks 3-4 and ongoing)

Check	Where	Target	Red flag
Reply rate on cold sends	Sequencing tool	> 5%	< 2% (may indicate spam folder placement)
Unsubscribe rate	Sequencing tool	< 0.3%	> 0.5%
Domain reputation	Google Postmaster Tools	High or Medium	Low
Sending volume trend	Sequencing tool	Gradual increase, no spikes	Sudden 3x+ volume jump

Google Postmaster Tools

Set up Google Postmaster Tools (postmaster.google.com) for every domain you send from. It shows:

Domain reputation (High, Medium, Low, Bad)
Spam rate (% of emails marked as spam by recipients)
IP reputation
Authentication pass rates (SPF, DKIM, DMARC)

Postmaster Tools rules:

Requires sending at least 100 emails/day to Gmail addresses to generate data. During early warmup, data may be sparse
Domain reputation should be "High" or "Medium" before scaling cold sends. "Low" means slow down. "Bad" means stop sending and diagnose
Spam rate should be < 0.1%. If it hits 0.3%+, Google will throttle your inbox placement

What Kills Warmup

Killer	What happens	How to prevent
Sending 200 cold emails on Day 1	Instant spam flagging. Domain reputation tanks before it's built	Follow the volume ramp. 5-10/day in week 1
High bounce rate (> 5%)	Mail providers see bounces as a sign of purchased/scraped lists. Reputation drops	Verify every email before sending. Use verified lists only
Spam complaints (> 0.3%)	Recipients flagging your email as spam directly damages reputation	Target the right ICP. Respect opt-outs. Don't email competitors or irrelevant contacts
Sending identical content to all recipients	Spam filters detect identical emails as a blast. Pattern-matched and flagged	Vary subject lines and openers. Use personalization tokens at minimum
Sending from multiple new inboxes simultaneously	5 new inboxes all ramping at the same time from the same domain looks like a spam operation	Stagger inbox warmup. Start inbox 1 on Day 1, inbox 2 on Day 7, inbox 3 on Day 14
Disabling warmup tool too early	The positive engagement signals from warmup stop. Reputation supported only by cold email (lower engagement)	Keep warmup running at maintenance level (5-10/day) permanently
Sending after hours or on weekends	Non-business-hour sending patterns are associated with spam bots	Send Mon-Fri, 7am-6pm in the recipient's timezone
Including links and images in every email	Link-heavy, image-heavy emails trigger spam filters	Plain text for cold email. One link max. No images. No HTML formatting

Warmup for Multiple Inboxes

When running outbound at scale, use multiple inboxes to stay under 50 cold sends per day per inbox.

Staggered warmup schedule

Inbox	Warmup start	Ready for cold	Daily cold volume
inbox1@mail.company.com	Day 1	Day 22	30-50/day
inbox2@mail.company.com	Day 7	Day 29	30-50/day
inbox3@mail.company.com	Day 14	Day 36	30-50/day
inbox4@mail.company.com	Day 21	Day 43	30-50/day

Total capacity at Day 43: 120-200 cold emails per day across 4 inboxes.

Multi-inbox rules

Stagger by 7 days minimum. Don't start all inboxes on the same day. Staggered starts look like natural team growth, not a spam operation
Each inbox should belong to a real person (or look like one). jane@mail.company.com is better than outbound1@mail.company.com. Real names, real signatures, real LinkedIn profiles linked
Different sending patterns per inbox. Don't send all 4 inboxes at 8:00am. Vary send times by 30-60 minutes. Different subject lines. Different email content. Identical patterns across inboxes trigger correlation-based spam detection
Monitor each inbox independently. One inbox can land in spam while the others are fine. Check placement per inbox, not just at the domain level

Warmup Content Rules

What to send during warmup

Phase	Content	Why
Week 1 (manual)	Real business emails. Conversations with colleagues, partners, vendors	Genuine engagement. The gold standard for reputation building
Week 1-2 (warmup tool)	The tool generates content automatically. No action needed	Automated engagement signals at scale
Week 2+ (first cold sends)	Follow cold-outbound-email-writing rules. Plain text. Short. Personalized	Cold email content should be indistinguishable from a real 1:1 email

Cold email content during warmup

Rule	Why
Plain text only. No HTML, no images, no banners	HTML emails trigger more spam filters. Plain text looks like a real email
One link maximum. No link in Email 1 if possible	Multiple links = spam signal. Minimize links during warmup
Short emails (60-80 words)	Short emails have higher engagement rates. Higher engagement = better reputation
Personalized subject lines and openers	Identical emails across recipients are pattern-matched as spam
No attachments	Attachments trigger spam filters, especially PDF and Office files
Sign with first name only. No banner image in signature	Image-heavy signatures trigger spam filters

Post-Warmup Maintenance

Warmup isn't done after 4 weeks. It transitions to maintenance mode.

Ongoing maintenance rules

Activity	Frequency	What to do
Warmup tool	Daily (permanent)	Keep at 5-10/day. Don't disable
Volume monitoring	Weekly	No sudden spikes. Ramp any volume increase over 2 weeks
Bounce rate check	Weekly	Must stay < 3%. If it spikes, pause cold and investigate
Spam complaint check	Weekly	Must stay < 0.1%. If > 0.3%, stop sending
Google Postmaster check	Weekly	Reputation should stay "High" or "Medium"
Blacklist check	Monthly	MXToolbox Blacklist Check. If listed, investigate and delist
SPF/DKIM/DMARC audit	Monthly	Especially after adding new sending tools

When to re-warmup

Trigger	Action
Paused sending for 30-60 days	Light re-warmup: 1 week of reduced volume
Paused sending for 60+ days	Full re-warmup: 2 weeks (see re-warmup plan above)
Domain got blacklisted	Resolve blacklist issue. Full re-warmup: 3-4 weeks
Switched email provider	1-week warmup on new provider. Domain history carries, IP doesn't
Bounce rate spiked above 5% on a send	Pause cold. Warmup-only for 1 week. Verify list quality
Spam complaint rate hit 0.5%+	Stop all cold sending. Investigate. Re-warmup for 2 weeks

Pre-Warmup Checklist

Before starting warmup:

[ ] Domain registered (new) or subdomain created
[ ] Email provider set up (Google Workspace or Microsoft 365)
[ ] SPF record configured with all sending services (per domain-setup-spf-dkim-dmarc skill)
[ ] DKIM configured for email provider AND sequencing tool
[ ] DMARC configured at p=none with reporting
[ ] Warmup tool selected and connected to the inbox
[ ] 5-10 known contacts identified for manual warmup emails in week 1
[ ] 10-15 industry newsletters subscribed to the inbox (for incoming engagement)
[ ] Google Postmaster Tools set up for the domain
[ ] First cold email list is verified and ready (don't verify 2 weeks early; verify just before first cold send)
[ ] Cold email templates written and reviewed (per cold-outbound-email-writing skill)
[ ] Daily send limit set in sequencing tool (start at 5-10, not 50)

Anti-Pattern Check

Sending 100 cold emails from a brand-new domain on Day 1. The domain has zero reputation. Every one of those emails lands in spam. The domain is now flagged. Follow the 4-week ramp. No shortcuts
No warmup tool, just manual emails. Manual emails are the best warmup, but you can't sustain 20+ manual emails per day for 4 weeks. Use a warmup tool for scale, manual for quality. Both together
Disabling warmup after 2 weeks because "it's working." The warmup tool provides ongoing positive engagement signals that keep your reputation healthy. Keep it running at maintenance level permanently
Starting all 4 inboxes on the same day. Stagger by 7 days. Four new inboxes ramping simultaneously from the same domain is a spam signal
Warming up with only the warmup tool (no real email). Warmup networks send synthetic engagement. Mix with real 1:1 email to look natural
Jumping from 20/day to 100/day in one week. Never more than 2x increase week-over-week. 20 → 40 → 80 is fine. 20 → 100 triggers spam filters
Not monitoring during warmup. Sending into a void. If your inbox placement dropped to 60% on Day 5, continuing to send makes it worse. Check daily in weeks 1-2
Sending HTML-formatted cold email during warmup. Images, banners, colored fonts, and embedded graphics trigger spam filters. Plain text only. One link max. No attachments
No SPF/DKIM/DMARC before warmup. Authentication must be set up BEFORE sending the first warmup email. Without it, warmup itself goes to spam and teaches providers your domain is untrustworthy

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# Email Warmup Strategy

## When Warmup Is Required

| Scenario | Warmup needed? | Duration |
|----------|---------------|----------|
| Brand new domain (just registered) | Yes, mandatory | 3-4 weeks minimum |
| New subdomain on existing domain | Yes | 2-3 weeks |
| New inbox on existing warmed domain | Yes (lighter) | 1-2 weeks |
| Existing domain, no cold email history | Yes | 2-3 weeks |
| Existing domain, paused cold email for 60+ days | Yes (re-warmup) | 1-2 weeks |
| Existing domain, sending consistently | No | Maintain sending volume. Don't spike |
| Switched email provider (Google → Microsoft) | Partial | 1 week. The domain has history but the IP is new |

---

## The 4-Week Warmup Plan

### Week-by-week volume ramp

| Day | Emails per day | Type of email | Engagement target |
|-----|---------------|--------------|------------------|
| 1-3 | 5-10 | Manual 1:1 email to known contacts (colleagues, partners, friends) | 100% open, 50%+ reply |
| 4-7 | 10-20 | Manual 1:1 + warmup tool (automated warmup network) | 80%+ open, 30%+ reply |
| 8-14 | 20-40 | Warmup tool + small cold batches (5-10 cold per day) | 60%+ open, 20%+ reply (warmup), monitor cold metrics |
| 15-21 | 40-60 | Warmup tool continues + increase cold to 20-30 per day | Monitor bounce rate (< 3%), spam complaints (< 0.1%) |
| 22-28 | 50-80 | Reduce warmup to maintenance level. Cold at target volume (30-50/day) | Stable inbox placement. Bounce < 3%. No spam spikes |
| 29+ | Target volume (30-50/day) | Warmup tool at maintenance (5-10/day). Cold at full volume | Ongoing monitoring |

### Volume ramp rules

- **Never more than 2x increase from one week to the next.** Going from 10/day to 50/day in one week is too fast. Go 10 → 20 → 40 → target
- **Include warmup volume alongside cold volume.** Don't replace warmup with cold. Run both in parallel during weeks 2-4. Warmup provides positive engagement signals that offset cold email's lower engagement
- **Daily send limit per inbox: 50 max for cold email.** Even after warmup, don't send more than 50 cold emails per day from a single inbox. Use inbox rotation for higher volume (see inbox-rotation skill)
- **Weekdays only.** Don't send warmup or cold email on weekends. B2B email is a weekday activity. Weekend sends look like spam bots

### What counts as warmup email

| Type | How it works | Engagement quality |
|------|-------------|-------------------|
| Manual 1:1 to known contacts | Email colleagues, partners, vendors. Real conversations | Highest. Real replies, real opens |
| Newsletter subscriptions | Subscribe the inbox to 10-15 industry newsletters. Open and click | Medium. Opens signal engagement to mail providers |
| Warmup tool (automated) | Service sends emails between accounts in a warmup network. Auto-opens, auto-replies, auto-removes from spam | Medium-high. Simulates real engagement at scale |
| Reply to inbound | Reply to any email the inbox receives. Newsletters, notifications, etc. | High. Real replies on real threads |

**Warmup email rules:**
- Manual 1:1 is the highest-quality warmup. Real conversations with real people. Mail providers reward this
- Warmup tools are the most scalable. They run in the background and generate engagement signals automatically. Use them for 80% of warmup volume
- Never use warmup-only email (no real sending at all). The pattern of only sending to warmup networks looks artificial. Mix real email (cold or manual) with warmup from Day 1

---

## Warmup Tools

### Major warmup tools

| Tool | How it works | Cost | Integrated with |
|------|-------------|------|----------------|
| Lemwarm (Lemlist) | Warmup network of Lemlist users. Auto-sends, opens, replies, removes from spam | Included with Lemlist paid plans | Lemlist |
| Mailwarm | Standalone warmup. Network of real inboxes | $69-159/month per inbox | Any email provider |
| Warmup Inbox | Standalone. Network-based warmup | $9-99/month per inbox | Any email provider |
| Instantly Warmup | Warmup network for Instantly users | Included with Instantly plans | Instantly |
| Smartlead Warmup | Warmup for Smartlead users | Included with Smartlead plans | Smartlead |
| Apollo Warmup | Basic warmup within Apollo | Included on some plans | Apollo |

### Tool selection

| Your situation | Best tool | Why |
|---------------|----------|-----|
| Already using Lemlist | Lemwarm | Included in plan. Integrated with sequencing |
| Already using Instantly | Instantly Warmup | Included. Tight integration |
| Already using Smartlead | Smartlead Warmup | Included. Native |
| Using Outreach or Salesloft (no native warmup) | Mailwarm or Warmup Inbox | Standalone tools that work with any provider |
| Budget-conscious, standalone | Warmup Inbox | Lowest cost standalone option |

### Warmup tool rules

- **Keep warmup running forever, not just during the initial ramp.** After the 4-week ramp, reduce to maintenance level (5-10 warmup emails per day). This maintains the positive engagement signals that keep your reputation healthy
- **Monitor warmup dashboard daily during weeks 1-2.** Most tools show inbox placement rate (what % of warmup emails land in inbox vs spam). Target > 95% inbox placement before starting cold sends
- **If inbox placement drops below 80% during warmup:** Stop cold sending. Continue warmup-only for 1 week. Check SPF/DKIM/DMARC. Check for blacklisting. Don't resume cold until placement recovers to > 90%

---

## Warmup by Domain Type

### New domain (just registered)

| Step | Timing | Action |
|------|--------|--------|
| 1 | Day 0 | Register domain. Set up Google Workspace or Microsoft 365. Configure SPF, DKIM, DMARC |
| 2 | Day 1-3 | Send manual 1:1 emails only. 5-10/day. Real conversations |
| 3 | Day 1 | Activate warmup tool. Start at 5-10 warmup emails/day |
| 4 | Day 4-7 | Increase warmup to 15-20/day. Continue manual emails |
| 5 | Day 8-14 | Warmup at 20-30/day. Start cold at 5-10/day |
| 6 | Day 15-21 | Warmup at 20-30/day. Cold at 15-25/day |
| 7 | Day 22-28 | Warmup at 10-15/day (maintenance). Cold at 30-50/day |
| 8 | Day 29+ | Warmup at 5-10/day (permanent maintenance). Cold at target volume |

**New domain minimum warmup: 3-4 weeks.** Don't rush this. A new domain has zero reputation. Building from zero takes time.

### New subdomain on existing domain

| Step | Timing | Action |
|------|--------|--------|
| 1 | Day 0 | Create subdomain. Set up SPF, DKIM, DMARC for subdomain |
| 2 | Day 1-3 | Manual 1:1 + warmup tool at 10-15/day |
| 3 | Day 4-10 | Warmup at 20-25/day. Start cold at 10-15/day |
| 4 | Day 11-21 | Warmup at 15-20/day. Cold at 25-40/day |
| 5 | Day 22+ | Warmup at 5-10/day. Cold at target volume |

**Subdomain warmup: 2-3 weeks.** The parent domain's reputation provides a slight head start, but the subdomain still needs its own sending history.

### Existing inbox re-warmup (paused 60+ days)

| Step | Timing | Action |
|------|--------|--------|
| 1 | Day 0 | Activate warmup tool at 10-15/day |
| 2 | Day 1-5 | Warmup only. No cold sending |
| 3 | Day 6-10 | Warmup at 15-20/day. Cold at 10-15/day |
| 4 | Day 11+ | Warmup at maintenance. Cold at target volume |

**Re-warmup: 1-2 weeks.** The domain has history but reputation decays during inactivity. A shorter ramp is sufficient.

---

## Monitoring During Warmup

### Daily checks (weeks 1-2)

| Check | Where | Target | Red flag |
|-------|-------|--------|----------|
| Inbox placement rate | Warmup tool dashboard | > 95% | < 80% |
| Bounce rate on cold sends | Sequencing tool | < 2% | > 3% |
| Spam complaint rate | Email provider admin | < 0.1% | > 0.3% |
| Blacklist status | MXToolbox Blacklist Check | Not listed | Any listing |
| SPF/DKIM pass rate | Email headers on test sends | 100% pass | Any failure |

### Weekly checks (weeks 3-4 and ongoing)

| Check | Where | Target | Red flag |
|-------|-------|--------|----------|
| Reply rate on cold sends | Sequencing tool | > 5% | < 2% (may indicate spam folder placement) |
| Unsubscribe rate | Sequencing tool | < 0.3% | > 0.5% |
| Domain reputation | Google Postmaster Tools | High or Medium | Low |
| Sending volume trend | Sequencing tool | Gradual increase, no spikes | Sudden 3x+ volume jump |

### Google Postmaster Tools

Set up Google Postmaster Tools (postmaster.google.com) for every domain you send from. It shows:
- Domain reputation (High, Medium, Low, Bad)
- Spam rate (% of emails marked as spam by recipients)
- IP reputation
- Authentication pass rates (SPF, DKIM, DMARC)

**Postmaster Tools rules:**
- Requires sending at least 100 emails/day to Gmail addresses to generate data. During early warmup, data may be sparse
- Domain reputation should be "High" or "Medium" before scaling cold sends. "Low" means slow down. "Bad" means stop sending and diagnose
- Spam rate should be < 0.1%. If it hits 0.3%+, Google will throttle your inbox placement

---

## What Kills Warmup

| Killer | What happens | How to prevent |
|--------|-------------|---------------|
| Sending 200 cold emails on Day 1 | Instant spam flagging. Domain reputation tanks before it's built | Follow the volume ramp. 5-10/day in week 1 |
| High bounce rate (> 5%) | Mail providers see bounces as a sign of purchased/scraped lists. Reputation drops | Verify every email before sending. Use verified lists only |
| Spam complaints (> 0.3%) | Recipients flagging your email as spam directly damages reputation | Target the right ICP. Respect opt-outs. Don't email competitors or irrelevant contacts |
| Sending identical content to all recipients | Spam filters detect identical emails as a blast. Pattern-matched and flagged | Vary subject lines and openers. Use personalization tokens at minimum |
| Sending from multiple new inboxes simultaneously | 5 new inboxes all ramping at the same time from the same domain looks like a spam operation | Stagger inbox warmup. Start inbox 1 on Day 1, inbox 2 on Day 7, inbox 3 on Day 14 |
| Disabling warmup tool too early | The positive engagement signals from warmup stop. Reputation supported only by cold email (lower engagement) | Keep warmup running at maintenance level (5-10/day) permanently |
| Sending after hours or on weekends | Non-business-hour sending patterns are associated with spam bots | Send Mon-Fri, 7am-6pm in the recipient's timezone |
| Including links and images in every email | Link-heavy, image-heavy emails trigger spam filters | Plain text for cold email. One link max. No images. No HTML formatting |

---

## Warmup for Multiple Inboxes

When running outbound at scale, use multiple inboxes to stay under 50 cold sends per day per inbox.

### Staggered warmup schedule

| Inbox | Warmup start | Ready for cold | Daily cold volume |
|-------|-------------|---------------|------------------|
| inbox1@mail.company.com | Day 1 | Day 22 | 30-50/day |
| inbox2@mail.company.com | Day 7 | Day 29 | 30-50/day |
| inbox3@mail.company.com | Day 14 | Day 36 | 30-50/day |
| inbox4@mail.company.com | Day 21 | Day 43 | 30-50/day |

**Total capacity at Day 43: 120-200 cold emails per day across 4 inboxes.**

### Multi-inbox rules

- **Stagger by 7 days minimum.** Don't start all inboxes on the same day. Staggered starts look like natural team growth, not a spam operation
- **Each inbox should belong to a real person (or look like one).** jane@mail.company.com is better than outbound1@mail.company.com. Real names, real signatures, real LinkedIn profiles linked
- **Different sending patterns per inbox.** Don't send all 4 inboxes at 8:00am. Vary send times by 30-60 minutes. Different subject lines. Different email content. Identical patterns across inboxes trigger correlation-based spam detection
- **Monitor each inbox independently.** One inbox can land in spam while the others are fine. Check placement per inbox, not just at the domain level

---

## Warmup Content Rules

### What to send during warmup

| Phase | Content | Why |
|-------|---------|-----|
| Week 1 (manual) | Real business emails. Conversations with colleagues, partners, vendors | Genuine engagement. The gold standard for reputation building |
| Week 1-2 (warmup tool) | The tool generates content automatically. No action needed | Automated engagement signals at scale |
| Week 2+ (first cold sends) | Follow cold-outbound-email-writing rules. Plain text. Short. Personalized | Cold email content should be indistinguishable from a real 1:1 email |

### Cold email content during warmup

| Rule | Why |
|------|-----|
| Plain text only. No HTML, no images, no banners | HTML emails trigger more spam filters. Plain text looks like a real email |
| One link maximum. No link in Email 1 if possible | Multiple links = spam signal. Minimize links during warmup |
| Short emails (60-80 words) | Short emails have higher engagement rates. Higher engagement = better reputation |
| Personalized subject lines and openers | Identical emails across recipients are pattern-matched as spam |
| No attachments | Attachments trigger spam filters, especially PDF and Office files |
| Sign with first name only. No banner image in signature | Image-heavy signatures trigger spam filters |

---

## Post-Warmup Maintenance

Warmup isn't done after 4 weeks. It transitions to maintenance mode.

### Ongoing maintenance rules

| Activity | Frequency | What to do |
|----------|-----------|-----------|
| Warmup tool | Daily (permanent) | Keep at 5-10/day. Don't disable |
| Volume monitoring | Weekly | No sudden spikes. Ramp any volume increase over 2 weeks |
| Bounce rate check | Weekly | Must stay < 3%. If it spikes, pause cold and investigate |
| Spam complaint check | Weekly | Must stay < 0.1%. If > 0.3%, stop sending |
| Google Postmaster check | Weekly | Reputation should stay "High" or "Medium" |
| Blacklist check | Monthly | MXToolbox Blacklist Check. If listed, investigate and delist |
| SPF/DKIM/DMARC audit | Monthly | Especially after adding new sending tools |

### When to re-warmup

| Trigger | Action |
|---------|--------|
| Paused sending for 30-60 days | Light re-warmup: 1 week of reduced volume |
| Paused sending for 60+ days | Full re-warmup: 2 weeks (see re-warmup plan above) |
| Domain got blacklisted | Resolve blacklist issue. Full re-warmup: 3-4 weeks |
| Switched email provider | 1-week warmup on new provider. Domain history carries, IP doesn't |
| Bounce rate spiked above 5% on a send | Pause cold. Warmup-only for 1 week. Verify list quality |
| Spam complaint rate hit 0.5%+ | Stop all cold sending. Investigate. Re-warmup for 2 weeks |

---

## Pre-Warmup Checklist

Before starting warmup:

- [ ] Domain registered (new) or subdomain created
- [ ] Email provider set up (Google Workspace or Microsoft 365)
- [ ] SPF record configured with all sending services (per domain-setup-spf-dkim-dmarc skill)
- [ ] DKIM configured for email provider AND sequencing tool
- [ ] DMARC configured at `p=none` with reporting
- [ ] Warmup tool selected and connected to the inbox
- [ ] 5-10 known contacts identified for manual warmup emails in week 1
- [ ] 10-15 industry newsletters subscribed to the inbox (for incoming engagement)
- [ ] Google Postmaster Tools set up for the domain
- [ ] First cold email list is verified and ready (don't verify 2 weeks early; verify just before first cold send)
- [ ] Cold email templates written and reviewed (per cold-outbound-email-writing skill)
- [ ] Daily send limit set in sequencing tool (start at 5-10, not 50)

---

## Anti-Pattern Check

- Sending 100 cold emails from a brand-new domain on Day 1. The domain has zero reputation. Every one of those emails lands in spam. The domain is now flagged. Follow the 4-week ramp. No shortcuts
- No warmup tool, just manual emails. Manual emails are the best warmup, but you can't sustain 20+ manual emails per day for 4 weeks. Use a warmup tool for scale, manual for quality. Both together
- Disabling warmup after 2 weeks because "it's working." The warmup tool provides ongoing positive engagement signals that keep your reputation healthy. Keep it running at maintenance level permanently
- Starting all 4 inboxes on the same day. Stagger by 7 days. Four new inboxes ramping simultaneously from the same domain is a spam signal
- Warming up with only the warmup tool (no real email). Warmup networks send synthetic engagement. Mix with real 1:1 email to look natural
- Jumping from 20/day to 100/day in one week. Never more than 2x increase week-over-week. 20 → 40 → 80 is fine. 20 → 100 triggers spam filters
- Not monitoring during warmup. Sending into a void. If your inbox placement dropped to 60% on Day 5, continuing to send makes it worse. Check daily in weeks 1-2
- Sending HTML-formatted cold email during warmup. Images, banners, colored fonts, and embedded graphics trigger spam filters. Plain text only. One link max. No attachments
- No SPF/DKIM/DMARC before warmup. Authentication must be set up BEFORE sending the first warmup email. Without it, warmup itself goes to spam and teaches providers your domain is untrustworthy