Inbox placement is the foundation everything else sits on. You can have the best list, the sharpest copy, and the best offer in your industry - and still fail completely if your emails land in spam. This is the playbook we run for every client before we send a single message.
Why deliverability is the silent killer
Roughly 95% of cold emails never reach the inbox. Gmail and Outlook AI filters have grown teeth. Spam complaints from one bad campaign can burn a domain for weeks. Send from your primary domain and you risk the whole company's email reputation.
Done right, deliverability is invisible. Done wrong, it kills every play that depends on it.
Domain strategy
We never send cold email from your primary domain. Ever. Instead we buy 5-15 secondary domains specifically for outbound, each closely matching your brand (yourbrand.io, yourbrand-team.com, get-yourbrand.com). They redirect traffic to your real site so they look legitimate to filters and to prospects.
- Primary domain stays clean for transactional and customer email
- Secondary domains are disposable - if reputation degrades, we rotate
- Each domain hosts 2-3 mailboxes - never more, to avoid sender reputation pooling
DNS authentication: SPF, DKIM, DMARC
Three protocols verify that the sender is who they claim to be. Without all three configured correctly, you're flagged as suspicious from the first send.
- SPF (Sender Policy Framework) - lists the mail servers authorised to send on behalf of your domain. Without it, providers can't verify the message came from you.
- DKIM (DomainKeys Identified Mail) - cryptographically signs each message so recipients can verify it wasn't tampered with in transit.
- DMARC (Domain-based Message Authentication, Reporting & Conformance) - the policy layer telling providers what to do with messages that fail SPF or DKIM.
We set all three on every secondary domain, with DMARC starting in monitoring mode (p=none) and tightening to quarantine once the domain has reputation.
The warmup process
New domains and mailboxes have zero reputation. Send 200 cold emails on day one and the domain gets cooked. We warm every mailbox for at least 2 weeks before any real outreach happens.
- Week 1 - 5 warmup emails per day per mailbox, ramping by 5/day. Reply rate target: 40%+ to signal real engagement to providers.
- Week 2 - Continue ramping to 30-40 warmup emails per day. By end of week 2 the mailbox is ready for real sends.
- Ongoing - Keep 10-15 warmup emails running per day even during real campaigns to maintain reputation.
Sending volume - the rules that don't bend
We cap real outbound at 30-40 emails per mailbox per day. Going higher gets you flagged. Gmail's hard limit is 500/day, Outlook's is 300/day - but those are theoretical maximums, not targets. Real-world sustainable volume is much lower.
Volume scales by adding mailboxes, not by pushing each mailbox harder. 10 mailboxes × 35/day = 350 sends/day with stable reputation. 1 mailbox sending 350/day = blacklist within a week.
Reputation hygiene
- Bounce rate target - under 2%. Always verify with Bounceban before sending.
- Spam complaint rate - under 0.1%. One bad list will kill a domain.
- List hygiene - re-verify lists every 3-6 months. Old data goes stale fast.
- Engagement metrics - watch open and reply rates. Drops of 30%+ vs baseline mean reputation is degrading.
Tools we use
Spaceship for bulk domain purchasing. Mailin for mailbox setup and warmup at scale. Smartlead, Instantly, EmailBison, or Lemlist for sending. Bounceban for pre-send verification. Mailreach or Glock Apps for inbox placement testing.
What to watch for
- Domain age matters - new domains (under 30 days) face heavier scrutiny. We buy domains 4-6 weeks before launch where possible.
- Workspace isolation - never share IP space across multiple domains. Each domain gets its own dedicated workspace.
- Replace domains every 9-12 months - even with perfect hygiene, reputation eventually decays. Plan for rotation.
- Don't send from sender names that look fake - generic-looking senders trigger filters faster than real ones.