[Vaultwarden] No invitation e-mail possible, due to permission issues [solved]

What type of hardware are you using: VPS bought online
What YunoHost version are you running: 12.1.7.1 testing
What app is this about: Vaultwarden

Describe your issue

When inviting a new user or doing the test e-mail from vaultwarden administration panel the error message below appears.

Sidenote: This is only one issue with newer versions of vaultwarden.
Allthough the web front-end works for old accounts, the browser extension and the Android app, cannot connect to the server anymore.

Share relevant logs or error messages

Error sending SMTP test email SMTP 5xx error: permanent error (553):
5.7.1 <vaultwarden-rs@myvaultwardendomain>: 
Sender address rejected: not owned by user vaultwarden

[SOLVED]: Not really, but in result yes. I did it the hard way: I purged the old installation and re-installed vaultwarden again. Then all issues with sending e-mails, access via extension or app were gone. If you have to do this, export your vault and re-import to the new installation. Importing works fine.

How did you proceed to purge the old installation?
You can put the procedure here, it might interest other people.
Thanks