Registration email relay through SMTP without credentials

I ran Discourse installation, everything went fine, I can access the Web INterface that ask for user and pw and want to sent test / registration email.

During the installation it has for a user and password, I put one " BUT" the SMTP relay server do not need one… I simply authorized the IP of the discourse server to relay…

So for now, the registration email can’t be sent…

How could I customized Discourse to relay through a SMTP without credentials ?

tks !!!

DISCOURSE_DEVELOPER_EMAILS: ‘name@example.com’
DISCOURSE_SMTP_ADDRESS: smtp.mailgun.org
DISCOURSE_SMTP_PORT: 587
DISCOURSE_SMTP_USER_NAME: postmaster@discourse.example.com
DISCOURSE_SMTP_PASSWORD: aUd34cdWKCu6CTjfoH7ykk

I don’t want to use a user and password. This SMTP relay server is simply are smart host and accept relay from the discourse IP. How do I set up Discourse to not authenticate ?