Email replies, routed only when the answer is certain

Inbound email is verified, and filed to an account only when the address unambiguously identifies one — otherwise it is held for a human rather than guessed.

What it is

The email half of the receiver. Signature and freshness are checked, the real author is taken from the From header rather than the envelope, and the account is resolved by a VERP address first and a uniquely-owned domain second. A domain shared by more than one account returns 'ambiguous' and the message is held.

Also called: email reply routing · reply went to the wrong company · shared email domain · inbound email

See it
Email replies, routed only when the answer is certain
Area
Platform & Admin
Group
Receiving
System
Customer Communications
Solves
3 named problems
01HMAC-SHA256 of (timestamp + token), with a 15-minute freshness window so a captured request is not replayable forever
02reply+{account}@domain wins outright; otherwise the domain must belong to exactly ONE account
03More than one owner returns ambiguous with the count, and the message is stored unrouted
Decision diagram: VERP address → account; unique domain → account; shared domain → held for triage. Sample data — no customer information appears here.
How it works
  1. 1HMAC-SHA256 of (timestamp + token), with a 15-minute freshness window so a captured request is not replayable forever
  2. 2reply+{account}@domain wins outright; otherwise the domain must belong to exactly ONE account
  3. 3More than one owner returns ambiguous with the count, and the message is stored unrouted
  4. 4The From header is preferred over the envelope sender, which legitimately differs for forwarders and relays
Why we built it

Several businesses share one sending domain, and the original approach filed a reply to the first account that looked like a match — which can put one builder's customer reply into a competitor's inbox. Holding a message for a human to place is recoverable; misfiling it is not. Inbound email is verified and filed to an account only when the address identifies one beyond doubt, and held for triage rather than guessed at when it does not.

The problem
  • Cross-account misfiling of customer replies
  • Replies lost on a fallback provider
  • Replayable webhook requests
Sound familiar?
What you get
Absolute isolation between accounts
An uncertain message is held, never guessed
Email replies survive a primary-provider outage

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