Allow SMTP connection without auth

[xavier-calland]

Describe the bug
It's not possible to use a SMTP server with anonymous connecion (like a local SMTP relay)

To Reproduce
Steps to reproduce the behavior:

1. Configure n8n with N8N_SMTP_HOST, N8N_SMTP_PORT and N8N_SMTP_SENDER but no N8N_SMTP_USER nor N8N_SMTP_PASS
2. Start n8n
3. Go to "User management"
4. The message "Set up SMTP before adding users (so that n8n can send them invitation emails)" is displayed and it is not possible to invite users.

Expected behavior
Allow SMTP configuration without configuration.

[nepodev]

You can enter dummy values for N8N_SMTP_USER and N8N_SMTP_PASS. If your SMTP server does not ask for a user and password, the values are not used. Works for my local SMTP.

[xavier-calland]

Yes, I tried this solution.
It works for some SMTP servers (like mailhog which I use in a development environment) but not the one I've to use on another environment.

As NodeMailer accepts configuration without authentication parameters, it seems like a good idea to use this behavior in N8N.

[Joffcom]

Hey @xavier-calland,

As you have opened a PR for this one I am going to mark this issue as closed as it is more of a feature than a bug and we can chat on the PR.

I do plan on getting the PR reviewed soon as well so this should be something that we have support for soon. Let me know if you have any questions on this.