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Mailbox providers decide where a message lands from two things: whether the sending domain proves the message is its own, and whether the message itself looks like careful automated mail. AsoBeast takes care of the message. The domain is yours to set up.

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What AsoBeast does for you

Every email AsoBeast sends carries the following. Alert emails are subscription mail. When WEB_PUBLIC_URL is https, each one also carries List-Unsubscribe and List-Unsubscribe-Post: List-Unsubscribe=One-Click (RFC 8058), so Gmail, Yahoo, Apple Mail and Outlook.com show their own unsubscribe button. Pressing it pauses that one email alert. The footer of every alert email links to the same choice on a confirmation page. Account emails (confirmation, password reset, invitation) and billing notices are transactional, so they carry no unsubscribe.

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What your domain needs

Publish three DNS records for the domain in SMTP_FROM. The examples use mail.example.com. SPF lists the servers allowed to send for the domain:
DKIM publishes the public key that verifies each message signature:
DMARC tells receivers what to do when neither check aligns with the visible sender, and where to send reports:
Gmail, Yahoo and Outlook.com require SPF, DKIM and an aligned DMARC record from anyone sending about 5,000 or more messages a day to their users, together with a working one click unsubscribe on subscription mail. Smaller senders should publish them anyway, because unauthenticated mail is the first to be filtered. Start DMARC at p=none, read the reports, and move to p=quarantine once they show only your own sources.

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Choose a relay

A managed relay such as Amazon SES, Postmark, Resend, Mailgun or SendGrid signs every message with DKIM for you, keeps reverse DNS correct and handles TLS. Point SMTP_HOST at it and publish the records it gives you. Running your own Postfix means you sign the mail, keep the reverse DNS of the sending address matching its hostname, and watch the reputation of that address yourself.

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Sign in AsoBeast instead

When the relay does not sign, AsoBeast can. Generate a key in the folder both Compose stacks mount:
Print the public half in the form the DNS record expects:
Publish that value as p= in the DKIM record above, then set SMTP_DKIM_DOMAIN, SMTP_DKIM_SELECTOR and SMTP_DKIM_PRIVATE_KEY_PATH and restart the API. The rules for the three variables are on the configuration reference. The signature covers both unsubscribe headers, which RFC 8058 requires.

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Set the sender name

Use a display name with an address on the authenticated domain, for example SMTP_FROM="AsoBeast <[email protected]>". Providers judge the display name too, and an address on another domain breaks alignment.

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Check a message

Send a test from Settings, Email alerts, then open the original message in the receiving client (“Show original” in Gmail). Look for spf=pass, dkim=pass with d= set to your domain, and dmarc=pass. An alert email should also show the List-Unsubscribe pair. Watch the spam complaint rate in Google Postmaster Tools. Keep it under 0.1% and never let it reach 0.3%.

Send alerts

Email and webhook delivery, and how unsubscribe works.

Configuration reference

Every SMTP variable and its rules.

Rotate secrets

What a new AUTH_SECRET does to unsubscribe links.
Last modified on October 10, 2026