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Ramp sending volume on new domains and IPs. Use when launching a new sending domain, switching providers, moving to a dedicated IP, or resuming sends after a pause.
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SOC 職業分類に基づく
Diagnose email problems and plan email infrastructure. Use when emails land in spam, bounce rates spike, deliverability drops, open rates decline, providers throttle sending, you need to set up email for a new product, or you're not sure which email skill to use.
Choose and configure an agent-native inbox provider for AI agents that send and receive email. Use when giving an AI agent its own email address, setting up two-way agent email communication, comparing agent inbox platforms, or adding guardrails to autonomous email workflows.
Build dashboards, alerts, and monitoring systems for email sending operations. Use when setting up deliverability monitoring, configuring alert thresholds, checking blocklists, building email metrics dashboards, or responding to deliverability incidents.
Classify inbound email replies by intent and route them appropriately. Use when building reply handling for outreach, support, or transactional email - detecting interested, not interested, OOO, bounce, unsubscribe, forwarded, and question replies.
Maintain email conversation context across messages using threading headers. Use when building thread reconstruction, linking replies to conversations, detecting thread hijacking, stripping quoted content, or providing thread context to AI agents.
Receive, parse, and process incoming email via provider webhooks. Use when setting up inbound email handling, parsing MIME messages, extracting content from replies, detecting threads, filtering spam on inbound, or routing incoming messages.
| name | email-warmup |
| description | Ramp sending volume on new domains and IPs. Use when launching a new sending domain, switching providers, moving to a dedicated IP, or resuming sends after a pause. |
| license | MIT |
Gradually ramp sending volume on new domains and IPs so mailbox providers trust you before you need to send at scale.
domain-authentication - SPF, DKIM, and DMARC must be in place before you start warming upsender-reputation - warmup builds initial reputation; this skill covers maintaining and recovering itrate-limiting - volume controls that protect reputation during and after warmupinbox-placement - factors beyond warmup that determine inbox vs spambounce-handling - processing delivery failures during warmup without compounding damageMailbox providers (Gmail, Microsoft, Yahoo) track sending behavior per domain and per IP. A domain or IP with no sending history is unknown - not trusted, not distrusted. When an unknown sender suddenly pushes thousands of messages, it looks indistinguishable from a spammer who just registered a fresh domain.
Warmup is the process of sending gradually increasing volumes of email to build a positive reputation before you need full throughput. Skip it and you'll hit deferrals, spam folder placement, or outright blocks that can take weeks to recover from.
In 2025, domain reputation is more important than IP reputation for most senders. Here's why:
Domain reputation follows you everywhere. When you switch providers (Postmark to SendGrid, SES to Resend), your domain reputation comes with you. IP reputation resets. Gmail and Microsoft shifted their filtering algorithms toward domain-centric signals starting in 2024, because domain reputation is harder to game - you can't just rotate to a new domain the way spammers rotate IPs.
IP reputation still matters, but less often. If you're on a shared IP pool (which most senders under 50,000 emails/month are), IP warming isn't your problem - the provider manages it. You only need to worry about IP warming when you move to a dedicated IP, which is typically only worth doing above 50,000-100,000 emails per month.
Every new combination needs warming. A warm domain on a new IP still needs IP warming. A warm IP with a new domain still needs domain warming. Changing both at once (new provider + new domain) is the hardest scenario.
| Scenario | What needs warming | Difficulty |
|---|---|---|
| New domain, shared IP | Domain only | Moderate |
| Existing domain, new dedicated IP | IP only | Moderate |
| New domain, new dedicated IP | Both | Hard - warm sequentially |
| Existing domain, new provider (shared IP) | Domain re-establishment | Easy-moderate |
| Resuming after inactivity | Domain re-warming | Easy-moderate |
The core principle: start low, increase gradually, never more than 2x the previous day's volume in a single jump. The exact numbers depend on your target volume.
This schedule assumes a new dedicated IP and new or low-reputation domain. If you're on a shared IP, you can be slightly more aggressive because the IP already has history.
| Day | Daily volume | Cumulative |
|---|---|---|
| 1 | 50 | 50 |
| 2 | 100 | 150 |
| 3 | 200 | 350 |
| 4 | 400 | 750 |
| 5 | 600 | 1,350 |
| 6 | 1,000 | 2,350 |
| 7 | 1,500 | 3,850 |
| 8 | 2,000 | 5,850 |
| 9 | 3,000 | 8,850 |
| 10 | 4,000 | 12,850 |
| 11 | 6,000 | 18,850 |
| 12 | 8,000 | 26,850 |
| 13 | 10,000 | 36,850 |
| 14 | 15,000 | 51,850 |
| 15-21 | 20,000-30,000 | - |
| 22-28 | 30,000-50,000 | - |
| 29+ | Full volume | - |
Key rules:
Cold outreach warmup is per-mailbox, not per-domain, because individual mailbox reputation matters for 1:1 sending.
| Week | Warmup emails/day | Cold emails/day | Total |
|---|---|---|---|
| 1 | 3-5 | 0 | 3-5 |
| 2 | 5-10 | 5 | 10-15 |
| 3 | 15-25 | 10-15 | 25-40 |
| 4 | 25-40 | 20-30 | 45-70 |
| 5+ | 30-40 | 30-50 | 60-90 |
Warmup emails here means messages to real contacts who will open and reply (colleagues, partners, newsletter signups). The goal is to generate engagement signals that establish the mailbox as a legitimate sender before you start cold outreach.
Cap cold outreach at 50 emails per mailbox per day. Going higher on a single mailbox dramatically increases the chance of triggering spam filters, regardless of how well you warmed up.
Transactional email (password resets, order confirmations, verification codes) gets more leeway from mailbox providers because recipients expect it. You don't need a strict day-by-day ramp, but you do need to be careful if volume is spiky.
mail.example.com for transactional, news.example.com for marketing) so marketing reputation problems don't block your password reset emailsThe recipients you choose during warmup matter as much as the volume. Mailbox providers weight engagement signals (opens, clicks, replies) heavily when evaluating a new sender.
Best warmup recipients (in order):
Never use during warmup:
SES has automatic IP warmup built in for dedicated IPs. When you provision dedicated IPs (standard), SES splits your traffic between dedicated and shared IPs, gradually increasing the dedicated IP percentage over 45 days. You don't need to manually control volume - SES handles the ramp.
For managed dedicated IPs, SES uses an adaptive strategy that warms per-ISP independently. If all your traffic goes to Gmail, SES considers the IP warm for Gmail but still cold for Microsoft. This is more sophisticated than time-based warming.
Domain warmup on SES is still your responsibility. SES automatic warmup only handles IP reputation. If you're using a new domain, you still need to ramp volume gradually.
SendGrid offers automated IP warmup that follows a predefined schedule when you enable it on a new dedicated IP. It starts at 50 emails/day and increases over 30-41 days. Excess volume is routed through shared IPs during warmup.
You can also manually control the warmup percentage if the automatic schedule doesn't fit your needs.
Postmark uses shared IP pools and focuses on domain reputation. There's no IP warmup to manage. If you're switching to Postmark with an existing domain, they recommend starting with your most engaged recipients and ramping up over 2-4 weeks. Postmark's account approval process itself acts as a gatekeeping step - they review your use case before you can send.
Resend uses shared infrastructure. No IP warmup needed. Focus on domain warmup - start with low volumes and ramp up. Their onboarding guides recommend beginning with transactional email (which has natural, organic volume growth) before adding marketing sends.
Use shared IPs if:
Use dedicated IPs if:
The in-between (50,000-100,000/month): Most providers recommend staying on shared IPs at this volume. Dedicated IPs need consistent volume to maintain reputation - if your sending is spiky (big campaigns some weeks, nothing other weeks), a dedicated IP will actually hurt you because the IP goes "cold" during low-volume periods.
Separate IPs for separate streams. If you use dedicated IPs and send both transactional and marketing email, use at least two IPs - one for each stream. A bad marketing campaign shouldn't block your password reset emails.
Monitor these signals daily during warmup. If any of them trigger, reduce volume immediately.
The receiving server is telling you to slow down. Common messages:
421 Too many connections from your IP450 Requested mail action not taken: mailbox unavailable421 Try again laterWhat to do: Reduce hourly sending rate. Add delays between messages. Do not retry aggressively - that makes it worse. Most deferrals resolve within 1-4 hours if you back off.
If open rates drop below 15-20% during warmup, you're either sending to unengaged recipients (fix your targeting) or your messages are landing in spam (check placement with seed testing).
Set up Google Postmaster Tools before you start warmup. It shows:
Note: Postmaster Tools data only appears after you're sending meaningful volume to Gmail (typically 100+ messages/day). You won't see data during the first few days of warmup.
AI agents introduce specific risks during warmup because they don't have the natural speed governors that human senders have. A loop that goes wrong, a retry bug, or a batch operation that triggers unexpectedly can spike volume and destroy a warming domain's reputation in minutes.
Critical safeguards for agent warmup:
Enforce rate limits at the infrastructure layer, not in agent code. Application-level rate limiting breaks under bugs - which is exactly when you need it most. Use a policy engine or provider-level limits that the agent cannot bypass.
Set hourly limits, not just daily limits. An agent that sends its entire daily allocation in 10 minutes looks like a spam blast to mailbox providers, even if the total volume is within your warmup target.
Use per-recipient cooldowns. An agent stuck in a retry loop can hammer the same recipient repeatedly. A cooldown window (e.g., 10 minutes per template per recipient) prevents this.
Monitor negative signal ratios, not just absolute counts. A risk budget that tracks bounces and complaints relative to send volume catches list quality problems early - before they compound into reputation damage.
Start agents on a domain with established reputation. Don't point a new AI agent at a brand-new domain. Warm the domain first with controlled, human-reviewed sends, then let the agent take over once reputation is established.
Services like molted.email provide infrastructure-level policy enforcement (rate limits, cooldowns, negative signal budgets, auto-pause) specifically designed for AI agent email sending, catching over-send scenarios before they damage your reputation.
Warmup builds initial reputation. Keeping it requires ongoing discipline.
Skipping warmup entirely. "We only send 500 emails a day, we don't need warmup." You do. Even low volumes on a brand-new domain with no sending history get filtered. Send 50/day for a week first.
Warming up without authentication. SPF, DKIM, and DMARC must be in place and passing before you send your first warmup email. Warming up without authentication is like trying to build credit with a fake ID.
Sending to your full list from day one. The most common mistake. People warm up for a week, then dump their entire 100,000-person list into a campaign. The sudden volume spike erases whatever reputation you built.
Ignoring deferrals and retrying aggressively. A 4xx response means "slow down." Retrying immediately or increasing retry frequency makes the problem worse. Back off and reduce volume.
Using purchased lists during warmup. Purchased lists have high bounce rates and low engagement. During warmup, when you have no reputation cushion, this is fatal. Use only opted-in contacts with recent engagement.
Warming the IP but not the domain (or vice versa). Both need warming independently. A new domain on a warm IP still needs domain warmup. Don't assume one covers the other.
Inconsistent sending during warmup. Sending 500 on Monday, 0 on Tuesday-Thursday, then 2,000 on Friday confuses mailbox providers. Send every day during warmup, at consistent volumes.
Not separating mail streams. Marketing and transactional email should be on different subdomains. If you warm up everything on one domain and then a marketing campaign generates complaints, your transactional delivery suffers too.
Stopping warmup emails when cold outreach starts. The warmup emails (to engaged contacts who open and reply) should continue alongside cold sends. They maintain the engagement signals that keep your reputation healthy.
Thinking warmup is a one-time event. If you stop sending for 30+ days, you need to re-warm. If you switch providers, you may need to re-establish domain reputation. Reputation decays without consistent positive signals.