Troublesome User Addition from Vaultwarden on Yunohost Instance - SMTP 5xx error: permanent error (535): 5.7.8 Error:

Describe the bug

I'm trying to add users on my Yunohost instance (which works) but impossible to add a user from Vaultwarden.

Error sending SMTP test email SMTP 5xx error: permanent error (553): 5.7.1 vaultwarden-rs@**domain.tld**: Sender address rejected: not owned by user vaultwarden Among the things I tried: I created another user and tried entering the credentials of this user (it didn't work).

I also obviously tried setting as address "vaultwarden@domain.tld" since the user is Vaultwarden, without success either... Do you have any idea? I would rather avoid using an external SMTP (it seems a bit ridiculous).

Thank you very much

Context

Hardware: VPS bought online
YunoHost version: 11.2.14 (testing)
I have access to my server: Through SSH
Are you in a special context or did you perform some particular tweaking on your YunoHost instance?: no
- If yes, please explain:
Using, or trying to install package version/branch:
If upgrading, current package version: can be found in the admin, or with yunohost app info $app_id

Steps to reproduce

sudo yunohost app install the_app

Expected behavior

I expected to be able to add users from Vaultwarden without any issues.

Logs

Please find the logs at this link: [insert log link here]

After sharing the log, please copypaste directly the link provided by YunoHost (to help readability, no need to copypaste the entire content of the log here, just the link is enough...)

[2024-06-09 10:45:41.171][vaultwarden::mail][ERROR] SMTP 5xx error: permanent error (535): 5.7.8 Error: authentication failed:  - Authentication credentials invalid
[2024-06-09 10:45:41.172][response][INFO] (test_smtp) POST /vaultwarden/admin/test/smtp => 400 Bad Request
[2024-06-09 10:50:21.447][request][INFO] POST /vaultwarden/admin/test/smtp
[2024-06-09 10:50:23.009][vaultwarden::mail][ERROR] SMTP 5xx error: permanent error (535): 5.7.8 Error: authentication failed:  - Authentication credentials invalid
[2024-06-09 10:50:23.010][response][INFO] (test_smtp) POST /vaultwarden/admin/test/smtp => 400 Bad Request

YunoHost-Apps / vaultwarden_ynh