What's new in October 2026

Create Campaign Endpoint With Idempotency-Key Support

The new POST /campaigns endpoint creates a draft campaign, so a campaign can now be created, sent and scheduled entirely through the API.

The content is either html_content, optionally with the Topol editor's json_content, or a template_id, whose HTML is copied onto the campaign. The request can also set the name or just the subject, the sender fields, reply_to, the audience in audience_config (all_contacts, list_ids, segment_ids, topic_id) and language_overrides for the secondary languages of a multilingual email.

Every email, list, segment and topic must belong to your team. Unknown audience_config keys return a 422, as does a language override for anything other than the email's secondary languages, and that error lists the allowed ones. The endpoint needs the campaigns:write scope, which full-access keys include, and sandbox keys can't use it.

An optional Idempotency-Key header works as it does on POST /emails. Repeating the request with the same key and payload within 24 hours returns the original draft with Idempotency-Replayed: true, whatever the order of the fields. A different payload returns 409 idempotency_key_conflict, and a retry while the first request is still running returns 409 idempotency_in_progress with Retry-After: 1. Sending and scheduling stay on the existing /send and /schedule endpoints.

The endpoint answers 201 with the same body as GET /campaigns/{id}. Campaign responses now also include audience_config and template_id, and the campaign detail adds json_content, so you can read back what you created.

Stricter Checks When Sending Or Scheduling Campaigns

Campaign send and schedule requests now refuse a campaign that can't go out instead of accepting it, so check these changes against your integration.

Send and schedule return 422 campaign_not_sendable with an explanation when the main sender's domain isn't verified for your team, when the audience has no subscribed contacts, or when your team has more contacts than its marketing plan allows. The first two used to be accepted everywhere and then fail during sending; the contact limit used to apply only in the web app, so API and MCP sends ignored it. Campaigns still don't count against your monthly sending quota. A scheduled campaign that is no longer sendable when it comes due is marked failed instead of being sent.

API keys limited to certain sending domains now apply that limit to campaigns too. Creating, sending or scheduling a campaign from any other domain, including a language's own sender, returns 403 domain_not_allowed, and the MCP tools return an error naming the domain.

Campaigns can now be scheduled at most one year ahead, in the API, MCP and the web app; later dates used to be accepted or fail with a 500. Unexpected errors on creating, sending or scheduling a campaign now return the error code internal_error instead of send_error.

Automatic Plain-Text Part For Template Sends And Campaigns

Emails sent with template_slug, including double opt-in confirmations, and all campaigns now go out with a plain-text version that Lettr generates from their HTML.

They used to be HTML only. Spam filters can count that against an email, and text-only mail clients had nothing to show. The text is generated for every campaign language and for test emails too. Merge tags survive the conversion, including inside links. The hidden preview text is left out, while sections set to show only on mobile are kept. If the conversion can't produce usable text, the email goes out HTML-only rather than failing.

A text field passed on an API send still takes precedence, and emails sent with your own html are unchanged. There is no setting to turn it off. The email page has a new Plain text preview tab, next to Desktop and Mobile, that shows the text that will be sent.

Passkeys As A Standalone Two-Factor Method

A new Passkeys switch in Settings → Two-Factor Auth makes sign-ins with a password, Google or GitHub ask for a passkey as the second step, even without an authenticator app.

With both an authenticator app and the switch on, either one works, and the challenge screen offers a recovery code as the fallback. Both methods share one set of recovery codes, and turning the switch on signs you out on your other devices.

Unlike a passkey on its own, the switch meets a team's “require 2FA” rule, so members held back by that rule can turn it on to comply. Under that rule, your last passkey can't be removed while it is your only two-factor method.

Adding a passkey or turning the switch on now needs your password or an existing passkey. An emailed code is accepted only for the first passkey of an account that signs in with Google or GitHub.

Sent Column With A Live Countdown On The Campaigns List

The Campaigns list has a new Sent column with the date and time each campaign went out.

Scheduled campaigns show their send time in blue with a countdown, such as “in 40 min” or “in 6 days”, and “Sending any moment” once the time has passed; hovering shows the full date and time zone. The list is now ordered by creation date, newest first, so editing an old campaign no longer moves it to the top.

Adamko Guided Tours For Multilingual Campaigns

Adamko can now guide you through setting up multilingual campaigns step by step in the app.

He offers four “Guide me” tours: choosing the contact property that holds each contact's language, building a multilingual campaign, setting your team's default communication language, and multilingual emails. He also answers questions about how languages are matched and which language a contact gets when theirs isn't available.