An SMTP relay sends your store's email from a provider whose whole job is delivery. Order confirmations land in the inbox and do not depend on your server's address.
- Get SMTP details
From your provider: host, port (usually 587), user and password, and verify your sending domain there (SPF and DKIM).
- Set them on the application
Email tab, SMTP: host, port, encryption (STARTTLS), user, password, from address and name. Everything PHP sends with mail() now goes through the relay.
- Send a test
The test email shows the provider's answer, so you see at once if the password or sender is refused.
This covers everything the store sends with PHP's mail(), including Magento and WordPress without any SMTP extension. If your store already has an SMTP extension, either works; do not set both to different providers.
To go back to the server's own mail server, clear the SMTP settings.
Did this solve it? If not, tell us what you see and we look at your server.
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