Send your campaigns with Postal in MailerPress

This feature requires MailerPress Pro 2.1.0 or later.

Postal is an open-source mail delivery platform that you host on your own server. Connect your Postal server to MailerPress to send your campaigns, automation emails and test emails, and to track bounces (emails returned as undeliverable, for example because the address doesn’t exist).

1. Prepare your Postal server

You need a running Postal installation that your WordPress site can reach over HTTP or HTTPS.

1. In the Postal web interface, open the mail server MailerPress should use.
2. Make sure your sending domain is configured and verified in Postal for this mail server.
3. Create a credential of type API (a Server API key) for this mail server and copy the key. MailerPress uses this secret key to send through your Postal server.
4. Note the base URL of your Postal installation, for example https://postal.example.com.

2. Link your site with the Postal API

1. Go to MailerPress > Integrations and open the Email Service Providers tab.
2. In Other Providers, click Configure on the Postal server card.
3. In Postal server URL, enter the base URL of your Postal installation, without the /api/v1 path.
4. Paste your key in Postal Server API key.
5. Fill in Default sender email address and Default sender name. The sender domain must be configured and verified in Postal. Empty fields show your global default sender as a placeholder.
6. Click Save changes. The button stays disabled until the server URL and the API key are filled in. The card moves to Configured Providers.
7. Turn on the card’s Enable toggle, then click Set as primary provider. The card shows the Primary badge: only the primary provider sends your emails.

3. Send a test email

1. On the Postal server card, open the Actions menu (three dots) and click Send test email.
2. Enter a recipient in Send to and click Send.

You should receive an email with the subject “This is a Sending Method Test”. If the test fails, MailerPress shows the error returned by Postal, for example:

• 401: check the Server API key configured for this Postal mail server.
• 403: the Server API key can’t send through this Postal mail server.
• 404: the endpoint wasn’t found. Check the Postal server URL.
• 503: Postal is temporarily unavailable. Try again later.

4. Configure the sending speed

MailerPress has no predefined sending profile for Postal. Set your own values to match your Postal server’s capacity:

1. Go to MailerPress > Settings > Sending frequency, or click Adjust sending frequency on the Postal server card.
2. Under Configuration Mode, choose Manual.
3. Set Emails per chunk (1 to 500), Interval between chunks (1 to 30 minutes) and Rate limit (emails per second).
4. Click Save settings.

Intervals shorter than 3 minutes can overload your WordPress server.

The sending frequency is saved for the provider that is primary at that moment. Set Postal as primary before you click Save settings. See How to change your sending frequency in MailerPress.

5. Enable bounce tracking

MailerPress learns about bounces through a webhook: a URL that Postal calls automatically when an email bounces.

1. On the Postal server card, click Configure.
2. Turn on Enable bounce tracking. The setting is saved immediately.
3. Under Webhook URL, click Copy. The URL looks like https://example.com/wp-json/mailerpress/v1/esp/bounce/postal.
4. In the Postal web interface, add a webhook to the same mail server with this URL.
5. Subscribe the webhook only to the MessageDeliveryFailed and MessageBounced events. Both mark the contact as bounced.

There is no secret to enter: MailerPress checks each notification’s signature with the public key your Postal server publishes at /.well-known/jwks.json. This address must be reachable from your WordPress site, otherwise MailerPress rejects the notifications.

6. Track your bounces

Go to MailerPress > Audience and click the Bounced tab of the contact list. Campaigns only go to subscribed contacts, so bounced contacts no longer receive them.

To compare Postal with the other sending services, see Choose and configure your email sending service.