Redmine

I would like to add a shared mailbox (office 365) as my emission email address in Settings>Email Notifications.

I've added the email through the UI and have also edited the /opt/bitnami/apps/redmine/htdocs/config/configuration.yml file to add

production:
email_delivery:
delivery_method: :smtp
smtp_settings:
enable_starttls_auto: true
address: "smtp.office365.com"
port: 587
domain: "mydomain.com"
authentication: :login
user_name: "testingmatt@mydomain.com"
password: ""

But as it's a shared mailbox there is no password, I feel this may be what's causing the error;

An error occurred while sending mail (535 5.7.3 Authentication unsuccessful [DB6PR07CA0004.eurprd07.prod.outlook.com] )

Has anyone got any ideas? Is it possible to get rid of the authentication?