KoltrixDocs

Receiving replies

Most transactional email is sent from noreply@ and every answer is thrown away. Koltrix works the other way round: a reply to a receipt, a password reset or a shipping notice comes back to your team inbox, where someone can answer it, and it is counted on the message it replied to.

You don't have to switch anything on.

Mail sent with the API or the SMTP relay

The From address of every API and SMTP send is a real mailbox in your workspace (that is why it has to be registered). So when someone presses Reply:

  1. The reply goes to your From address and arrives in your team inbox, in that mailbox, for whoever has access to it.
  2. It is threaded with the message you sent, which is in the mailbox's Sent folder.
  3. Koltrix matches the reply's In-Reply-To and References headers to the message and records it: reply_count goes up, replied_at is set the first time, engagement_score goes up by 10, and a reply event is added to the message's timeline.
curl https://api.koltrix.com/api/v2/messages/6f1c2a9e-3b7d-4e41-9a52-0c8d1f3e7b20 \
  -H "Authorization: Bearer $KOLTRIX_KEY"
{
  "id": "6f1c2a9e-3b7d-4e41-9a52-0c8d1f3e7b20",
  "to": "[email protected]",
  "subject": "Your receipt for order 1042",
  "status": "sent",
  "reply_count": 1,
  "replied_at": "2026-10-02T15:12:40Z",
  "engagement_score": 12
}

(Abridged; the full response is in Sending email.)

A reply is the most reliable engagement signal there is. An open can be triggered by a mail provider fetching images, and a click by a link scanner; a reply needs a person.

If replies should go somewhere else, such as an existing helpdesk, send from an address whose replies you forward there, or set up Settings → Forwarding for that mailbox.

Mail sent from the Koltrix app

Messages your team sends from the Koltrix app also carry a signed reply address in their Reply-To header:

Reply-To: reply+<message id>.<signature>@<your sending domain>

The signature is a keyed hash that only your workspace can produce. Without it, anyone could guess addresses and attach mail to another conversation. A reply with a missing or wrong signature is delivered as ordinary mail rather than threaded, and a valid address from one workspace can't thread a reply into another. The address uses plus-addressing on your existing domain, so there is no extra mailbox and no extra DNS record.

A reply to that address is threaded under the original message and counted on it, and is always filed in the inbox, never in spam: you wrote to this person first.

Unsubscribe by reply

If a reply to a signed reply address says little more than "unsubscribe", "take me off this list" or "stop emailing me", the sender is added to your suppression list with the reason unsubscribe.

Two kinds of reply are deliberately not treated as a request:

  • Quoted text. Almost every newsletter footer contains the word "unsubscribe", so the quoted part of a reply is ignored.
  • A real message that mentions unsubscribing. "Can you check whether we were unsubscribed by mistake?" is a question for a person. Only a short reply, under 200 characters once the quote is removed, that says essentially nothing else counts.

Someone who can't find your unsubscribe link reaches for "Report spam" instead, and a spam complaint costs your domain's reputation far more than one lost subscriber.

If replies don't arrive

  • Check the domain's MX record. Replies reach Koltrix only if your domain's MX record points to mail.koltrix.com. See Custom domains and DNS.
  • Check who can see the mailbox. A reply lands in the mailbox it was sent to. Teammates without access to that mailbox won't see it.
  • Check Spam. A reply that isn't matched to a message you sent goes through the normal spam filter like any other mail.

Still stuck? Email [email protected] with the message id.