Reputation Firewall

Cold email can't break your product emails.

Truncus enforces isolated email streams. Transactional and outreach traffic run on separate domains with separate reputations. Hard API enforcement — not guidelines.

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The problem nobody talks about

Most email providers let you send any type of email through any domain. Transactional, marketing, cold outreach — all sharing the same sending reputation.

When a cold email campaign generates complaints, your password reset emails start landing in spam. This isn't theoretical. It happens to SaaS companies every day. And by the time you notice, your domain reputation is already damaged.

The fix isn't "be careful." The fix is architecture.

How Truncus solves this

┌─────────────────────────────────────────────┐
│ Your App                                     │
├──────────────────┬──────────────────────────┤
│ Transactional    │ Outreach                  │
│ Stream           │ Stream                    │
│                  │                           │
│ auth emails      │ cold outbound             │
│ billing          │ ColdCopy campaigns        │
│ onboarding       │ prospecting               │
│                  │                           │
│ Protected        │ Expendable                │
│ reputation       │ reputation                │
└───────┬──────────┴──────────┬───────────────┘
        │                     │
   mail.acme.com       outreach.acme.com
        │                     │
   Never mixed           Rotatable

Each stream has its own domain, its own reputation score, and its own metrics. Traffic cannot cross streams. The API enforces this at the infrastructure level.

Hard enforcement, not best practices

This isn't a documentation recommendation. It's enforced at the API level. If you try to send cold outreach through a transactional domain:

{
  "error": "domain_type_mismatch",
  "message": "Cold outreach is not allowed on a transactional domain.",
  "recommended_fix": "Use a dedicated outreach domain."
}

No warnings. No silent fallback. Your transactional reputation stays clean.

Most email APIs don't protect you

No isolationMost email APIs let all email share the same domain reputation. One bad campaign poisons everything.
Not enforcedSome offer categories or labels, but nothing stops you from sending cold outreach through your auth domain.
No outreach streamEven APIs with transactional/broadcast separation have no concept of cold outreach as a separate, expendable stream.
TruncusHard enforcement. Isolated streams. Cold email can never touch transactional domains.

What this means for you

Run cold outreach campaigns without risking your auth email deliverability
Rotate outreach domains without affecting product email
See separate health metrics per stream — know exactly where issues come from
Sleep at night knowing a ColdCopy campaign can never break your password resets

Your product emails deserve protection.

Stream isolation is included on all plans. No setup fee. No compromise.

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Stream Isolation — Isolated Email Streams | Truncus