Deliverability and suppressions
Whether your mail reaches the inbox depends mostly on two things: your domain's DNS, and whether you keep mailing people who don't want your mail. Koltrix handles as much of both as it can for you. This page explains what it does and what is left to you.
Your domain
Publish the five records in Custom domains and DNS. They prove the mail is really from you:
- SPF says Koltrix's servers may send for your domain.
- DKIM signs every message. Koltrix gives each domain its own 2048-bit key and signs outbound mail on its servers; you publish only the public half and never handle the private key.
- DMARC tells receiving providers to treat unsigned mail claiming to be from you as suspect.
A domain sends only once all five records check out.
The suppression list
The suppression list is the set of addresses your workspace will not mail. It applies to everything the workspace sends: the API, the SMTP relay, broadcasts, sequences and the Koltrix app. A send to a suppressed address is skipped silently; the rest of the recipients still get the message.
An address is added automatically when:
| Reason | How it happens |
|---|---|
bounce | The recipient's provider permanently rejected a message (a 5xx reply, or a bounce report that comes back later with a 5.x.x status). Temporary failures (4xx) never suppress. |
unsubscribe | The person clicked the unsubscribe link in a broadcast or sequence, was unsubscribed through the API, or replied asking to be removed. |
You can see and edit the list under Settings → Blocked senders, in the section We won't email these. Add an address there to stop mailing it, or remove one to mail it again.
Before you remove a bounced address, check that the reason has gone away. If the mailbox still doesn't exist, the next message bounces and the address is suppressed again, and repeated bounces hurt your domain's reputation.
Unsubscribe links
Broadcasts and sequence emails get an unsubscribe link in the body and a
List-Unsubscribe header, which lets mail providers show their own
"Unsubscribe" button. Clicking either unsubscribes the person from the list and
adds them to the suppression list.
Transactional mail sent with the API or the SMTP relay doesn't get an unsubscribe link: receipts and password resets are mail people asked for. If you send something closer to marketing through the API, add your own link.
Tracking
| Opens | Clicks | |
|---|---|---|
| REST API | Yes: a 1×1 image is added to the HTML part | No |
| SMTP relay | No | No |
| Broadcasts | Yes | Yes: links are rewritten through Koltrix |
| Sequences | No | No |
Opens are counted only when a person seems to have opened the message. Mail
providers that fetch every image as soon as a message arrives (Apple Mail
Privacy Protection, Gmail's image proxy and corporate scanners among them) are
recorded in the message's events with "prefetch": true but not counted. Even
so, treat open rates as a rough signal. Clicks and, above all,
replies are the reliable ones.
New domains
A new domain has no sending history, and receiving providers are wary of a domain that suddenly sends thousands of messages. Koltrix paces broadcasts, sequences and app sends from a new domain with a daily cap that rises over its first weeks. A broadcast that would go over today's cap is paused rather than sent in part, and a sequence step waits for the next day.
You can help:
- Start with mail people expect: receipts, sign-in links, replies to people who wrote to you.
- Send broadcasts to recent, engaged subscribers first.
- Use double opt-in for any list people can join from a public form.
Checking a message
- Settings → Logs shows every outbound message with its status, and the receiving server's reply for anything that bounced.
- mail-tester.com scores a message you send to it and names anything misconfigured. Aim for 9 or 10 out of 10.
- If one provider puts your mail in spam and the others don't, look at that provider's postmaster tools (Google Postmaster Tools, Microsoft SNDS).