Deliverability & karma
Postern is positioned as two-way transactional and agentic mail — not cold-outreach volume. That framing drives every deliverability control: the goal is that an agent’s real, expected mail lands, and that one misbehaving agent can’t poison the pool.
Authenticated sending
Section titled “Authenticated sending”Every Postern mailbox sends through Azure Communication Services as an authenticated sender, registered at create time. That means:
- SPF + DKIM pass, aligned to the sending domain;
- DMARC is published at least
p=none, aligned; - behind an NS-delegated zone, our DNS auto-serves the DKIM CNAMEs, SPF, and MX so authentication is correct without you adding records.
This is why a Postern send doesn’t bounce the way a raw SMTP relay would — the authentication story is handled before the first message goes out.
2026 bulk-sender rules, enforced platform-wide
Section titled “2026 bulk-sender rules, enforced platform-wide”Postern enforces the Gmail / Yahoo bulk-sender requirements across the whole platform, so you inherit compliance instead of implementing it:
| Requirement | How Postern meets it |
|---|---|
| SPF + DKIM pass | Authenticated ACS sender + served DNS records |
DMARC ≥ p=none, aligned | Published per domain (delegated or manual) |
| One-click unsubscribe (RFC 8058) | Added on subscribed mail |
| Low complaint rate | Auto-throttle + kill-switch keep complaints <0.1% (hard ceiling <0.3%) |
Ramping send caps
Section titled “Ramping send caps”New mailboxes don’t get full volume on day one. Per-mailbox daily send caps ramp as a mailbox proves itself — roughly 5–10/day to start, climbing to 30–50/day over weeks. This mirrors how warmed infrastructure behaves and keeps a fresh address from tripping spam heuristics.
Karma — throttle, don’t blunt-cap
Section titled “Karma — throttle, don’t blunt-cap”Instead of a single hard ceiling, Postern tracks karma per agent. Sends spend karma; replies earn it back. A high-karma agent (the kind that holds real two-way conversations) gets more headroom; a low-karma agent (one that only blasts and never gets replies) gets throttled. The effect: legitimate transactional patterns are rewarded, and one-directional spray is naturally slowed without punishing fan-out across many mailboxes.
Reputation segmentation
Section titled “Reputation segmentation”Reputation is segmented per subdomain, each with its own DKIM. One bad agent’s blast radius is
contained to its subdomain rather than the whole pool. Reputation-sensitive cohorts route to
isolated spring* domains so a risky workload can’t drag down a healthy one. segmentation by design
Auto-throttle & kill-switch
Section titled “Auto-throttle & kill-switch”Postern watches bounce and complaint signals continuously. A spike triggers automatic throttling and, past a threshold, a kill-switch on the offending mailbox or agent — before the pool’s reputation is damaged. This is enforcement, not advice: it happens platform-side without you wiring anything.
- Domains & onboarding — the DNS authority these controls use.
- Rate limits & quotas — the concrete numbers and headers.
- x402 test mode — economic anti-abuse alongside karma.