Not currently, the only workaround is to run something like GitHub - maildev/maildev: SMTP Server + Web Interface for viewing and testing emails during development. or GitHub - mailhog/MailHog: Web and API based SMTP testing with auto forwarding.
You set it up with a basic user/pass and set the upstream to your relay without auth. Then connect n8n to e.g.
Or of course add a user account on your mail relay…