Sending email via Office365

When sending an email using office365 smtp the user_name needs to be the same as the value used in the from of the email. Otherwise you will get: Client does not have permissions to send as this sender

Mail.defaults do
  delivery_method :smtp, { 
    address: 'smtp.office365.com',
    port: 587,
    user_name: ENV['OFFICE_365_SMTP_USER'],
    password: ENV['OFFICE_365_SMTP_PASSWORD'],
    authentication: :login,
    encryption: :tls
  }
end

mail = Mail.new do
  from    ENV['OFFICE_365_SMTP_USER'],
  to      '[email protected]'
  subject 'This is a test email'
  body    'This is a mail body'
end

mail.deliver