SQL 2014 - reports subscriptions failing

Hello!!

I'm working on SQL 2014 and was told that I can't use Office 365 directly as it does not support SMTP authentication. I had setup gmail account added the office365 account and setup smtp relay using sendgrid..

I can send emails from gmail as the office365 account, but the SSRS subscriptions are failing..

'Failure sending mail: Mailbox unavailable. The server response was: Unauthenticated senders not allowed"

can you please let me know what I am missing?

thank you!