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OpenCart email with Groundmail

Send OpenCart store email through Groundmail by switching OpenCart's mail engine to SMTP and pointing it at the Groundmail SMTP relay. Order confirmations, order status updates, customer account and password reset emails, and admin alerts then go out from your own domain. These steps cover OpenCart 4.

Updated Nov 14, 20262 min read

Prerequisites

  • A Groundmail account with a verified sending domain.
  • An SMTP credential: in the Groundmail dashboard, open SMTP and choose Create SMTP credential. The password (gmsmtp_…) is shown once, so copy it. See SMTP relay.
  • Admin access to OpenCart, with permission to edit store settings.

Everything the store sends through the relay goes out as transactional email, so use it for order, account and notification email. Send opt-in newsletters through the API with category: "newsletter" once your account is approved, and never send cold email.

Set the mail engine

  1. In the OpenCart admin, go to System, then Settings, and edit your store.
  2. Open the Mail tab and fill in:
OpenCart field Value
Mail Engine SMTP
SMTP Hostname tls://smtp.groundmail.dev
SMTP Username groundmail
SMTP Password Your SMTP credential (gmsmtp_…)
SMTP Port 587
SMTP Timeout 5 or more
  1. Leave Mail Parameters empty, and click Save.

The tls:// prefix makes OpenCart upgrade the connection with STARTTLS, which is what the relay expects on port 587. Don't use ssl://, which is for port 465. Some OpenCart 4 releases group these fields under an SMTP heading and label them Hostname, Username, Password, Port and Timeout.

Match the sender

On the Store tab of the same settings page, set E-Mail to an address on your verified domain, such as orders@yourdomain.com. OpenCart sends store emails from it.

Test it

OpenCart has no test button for mail settings, so send a real store email to one of Groundmail's simulator addresses. They work over SMTP and never reach a real inbox. Register a customer account, or place a test order, with the email:

delivered@simulator.groundmail.dev

Then confirm in Groundmail: open Emails in the dashboard, or run:

Terminal
curl "https://api.groundmail.dev/emails?limit=5" \
  -H "Authorization: Bearer $GROUNDMAIL_API_KEY"

The email appears with the status delivered and "test": true. Use bounce@simulator.groundmail.dev to see a hard bounce. The full list is in Testing. Send errors show in the admin under System, Maintenance, Error Logs.

Troubleshooting

Connection timed out or the TLS handshake fails. Check the hostname is tls://smtp.groundmail.dev (with the prefix) and the port is 587. If your host blocks outbound port 587, use 2525 with the same settings.

Authentication failed. The username must be exactly groundmail, and the password must be the SMTP credential (gmsmtp_…), not an API key (gm_…).

The message is rejected because of the From address. The store E-Mail must use a verified domain on your account. Until then you can only send from the sandbox sender, and only to your own account email.

A recipient never receives the email. The address may be on your suppression list, usually after a hard bounce. See Suppressions, and create a webhook for email.bounced to get notified.

Sends are deferred. A new account has a daily ramp-up limit, and the Free plan has a daily limit. The relay replies with a temporary error and a retry time. See Sending limits.

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