SMTP relay with IIS

We want to create an alias to send alert from our backup application:

What we need;

• A user with exchange online license
• IIS SMTP service installed
• THe SPF record with public IP that send to 365.

Install SMTP service (add the feature with server manager) and set it with automatica start:

Go to Exchange online console and create a new mail-enabled  security group

Give to it the send as permession for the selected user

Add the 

Configure SMTP service:

Go to properties:

Set who is autorized to realy:

Under "delivery" tab set the authentication: