How to Set Up SMTP Relay

How to Set Up SMTP Relay

Overview

Configure an SMTP Relay so that Horizon sends emails directly through your own mail server, improving deliverability and ensuring emails arrive as your address — not ours. This is especially important for calendar invites and other time-sensitive emails.

Prerequisites

  • Your SMTP server hostname (e.g., smtp.mailgun.org)
  • Your SMTP port (typically 587 for TLS or 465 for SSL)
  • Your SMTP authentication username and password

Steps

  1. In Horizon, navigate to Mail > SMTP Relay.
  2. In the SMTP Server section, enter your Hostname, Port, and select your Encryption type (TLS is recommended).
  3. Enter your SMTP Username and Password.
  4. Ensure the Active toggle is enabled, then click Save.
  5. Click Send SMTP Relay Test in the top-right corner and enter an email address to verify the configuration is working.

Result

Outgoing emails from Horizon are routed through your SMTP server. If a test email was sent, you will see a success notification and the email will arrive in your inbox from your configured address.