The PAM 3.X GUI requires that an account be selected under the Credential Manager SMTP Email Server settings, even if SMTP Authentication will not be used. Optionally any account can be selected here as a placeholder, but if no authentication is being used for the SMTP server then a dummy (fake) account is recommended.
Benefits of a dummy account:
Any PAM 3.x
SMTP Server with no authentication required
To create a "dummy account" and use it for SMTP follow these steps:
Documentation on configuring Password Management emails: