Postmark

Postmark uses a single Server API token for both transports, and its webhooks report what happened after the handoff: confirmed deliveries, bounces, and spam complaints. Those events power the delivered state, webhooks like mail.delivered and mail.bounced, and automatic suppressions.

Before you start

• A Postmark server with your sender domain verified (DKIM and Return-Path). See Deliverability for what each record proves.
• The server’s Server API token (the server’s API Tokens tab).

Add the account in Mailway

1. Add the provider.

   In the console, open Providers → New provider, pick Postmark and paste the Server API token. Secrets are encrypted at rest. The one token gives the account both transports: mail that reaches Mailway’s SMTP relay goes on over Postmark’s SMTP server (smtp.postmarkapp.com, with the token as both login and password), and HTTP API and console mail go over Postmark’s API.

   Tip

   Leave Send via on Auto. Set to API only, relayed mail can’t be handed over as-is, because Postmark’s API is structured-only. It then skips the account unless a project admin enables re-encoding on the attachment.

2. Attach it to a project.

   Open the project, attach the provider, and position it in the failover order. Send something, and the provider health panel starts filling in.

Delivery events

Without delivery events, Postmark only reports that it accepted the mail. With them, Postmark tells Mailway what happened afterwards.

Postmark doesn’t sign its webhooks, so Mailway protects the URL two ways: Postmark logs in with a username and password Mailway generated for this provider, and Mailway checks that each request comes from Postmark’s published webhook addresses.

1. Open delivery tracking. In the console, open the provider → Delivery tracking (beside Configure). Mailway creates the provider’s webhook URL and shows it with a username and password. Treat the password like any other secret. Regenerating (at the bottom of the dialog) rotates the credentials and revokes the old ones instantly, so update Postmark afterwards.

2. Add the webhook in Postmark. On your server, open the Transactional message stream → Webhooks → Add webhook:

   • Webhook URL: paste the URL.
   • Open Custom headers and basic auth → Basic auth credentials: paste the username and password.
   • Events: tick Delivery, Bounce, and Spam Complaint. Open, Link Click, and Subscription Change can stay off, because Mailway ignores them.
   • Leave both Include message content boxes off. Mailway already keeps the message, so there’s no reason to send it again with every event.

What each event does in Mailway

Postmark event	Mailway outcome
Delivery	The mail turns delivered (confirmed by the provider’s event).
Bounce: hard bounce, bad address, manually deactivated	The mail turns bounced; the address is auto-suppressed for the project.
Bounce: soft bounce, transient, DNS error, blocked	Recorded as soft_bounced (temporary; a later delivery outranks it).
Bounce: auto-reply, subscribe / unsubscribe notices	Ignored, because it isn’t a delivery outcome.
Spam complaint	The mail turns complained; the address is auto-suppressed.

Note

Postmark’s events identify a message by its MessageID. For API sends, Postmark returns that id at handoff. Postmark’s SMTP reply doesn’t include it, so for SMTP sends Mailway adds a Postmark metadata header (X-PM-Metadata-mw) carrying the mail’s id. Postmark echoes it back in every event and removes the header before delivery. If your message already has an X-PM-Metadata-mw header, Mailway’s value replaces it (other X-PM-Metadata-* keys you set are left alone). Both transports correlate exactly (verified live). An event only ever affects mail your own team sent through that provider. An uncorrelated event is still recorded and visible, just not pinned to a specific mail.

Check the connection

• Connection check. The provider page’s connection check logs in over SMTP and makes one read-only API call, without sending anything.
• Delivery events. Save the webhook and use Send test on Delivery in Postmark: the sample event is accepted, and the Delivery tracking dialog’s last step ticks when it arrives. After a real send, the mail’s timeline shows the delivered or bounced step with Postmark’s own details attached.

What Postmark changes

Mailway hands Postmark the message your app sent, byte-for-byte apart from the automatic exceptions, and archives it with the same exceptions made on receipt. Postmark then builds its own message from them: a new Message-ID and Date, a re-encoded body, and any DKIM signature your app applied is removed. Postmark signs with its own DKIM for your domain. Tested results: What providers change.

Limits

Your Postmark plan’s own sending limits apply. Mailway adds none for Postmark beyond your Mailway plan’s quotas.

Postmark's free plan past its monthly limit

Once the free plan’s monthly limit is used up, Postmark still accepts mail on both transports, 250 over SMTP and 200 OK with a message ID over the API, but doesn’t deliver it: the mail doesn’t show in Postmark’s activity, and no bounce or other event comes back (tested 2026 Q4). To Mailway this looks like any accepted mail, so it stays Accepted and doesn’t fail over.

To keep mail away from Postmark past the limit, set three things on the provider in Mailway: Free tier to your plan’s limit, Resets on day to the day your Postmark billing period starts, and Stop at the free tier on. When you add a Postmark account, the console fills in the free plan and turns the stop on. For an account you added earlier, turn it on yourself. Once Mailway’s count reaches the free tier, Mailway sends nothing through Postmark until the free tier resets, and mail goes to the project’s other providers instead. A mail with no other provider, or one pinned to Postmark, is retried for about 50 minutes, then marked Exhausted. Mailway also emails your team when its count reaches 80% and 100% of the free tier.

Mailway counts one per recipient (To, Cc and Bcc), because Postmark counts each Cc and Bcc address as an email. The count is approximate and covers only mail sent through Mailway. Mail sent on the same account from elsewhere uses up the plan sooner, and mails sent at the same moment near the limit can pass it. For mail that must arrive, don’t rely on Postmark’s free plan.