MS Outlook 365 Connected System not working

Hello Appian expert,

We want to send emails from Appian using Outlook 365 account.

For that, we tried using MS Outlook 365 connected system and followed all the account set-up steps. but the connected system is not able to validate credentials and returns 'Invalid Access'

Steps: 

1. Login to Azure AD, go to ‘App Registration’ and create a new app. Use the generated Client ID and Tenant ID from that app into the connected system
2. Generate client secret from ‘Certificates and Secrets’ and pass it as input
3. In the ‘API permissions’ option, click on ‘Add permission’ > select the Microsoft Graph API > Add (Application) Mail.Send permission
4. Use emailaddress@domain.onmicrosoft.com email id

To confirm, we are able to use the same account using MS Graph Explorer and successfully send emails.

My questions:

1. Have you used this connected system and if so, please share any of the steps we missed?

2. What are the alternative options to send Appian emails from an EWS 365 account?