Now with this I get notification for both when a new message comes into the mailbox and also when an email is sent out from the mailbox. Following are some of the options I have tried to differentiate between sent email vs received email.
1. During subscription use users/email address removed for privacy reasons/mailFolders('inbox')/messages . This sends notification only when there is a new email in the inbox. If any folders are inside inbox, then we'll need to subscribe for all those folders which may be tedious when you have lots of mailboxes.