Mail flow policy requirement:
I’m trying to use mail flow policy but there is no option to notify sender. (notify policy tip is not ok, should be able to input custom text to notification)
Please advise if there is other option for this.
Have you looked at DLP policies, as an alternative, to see if that is any better?
WIth DLP, it can block emails that match financial data and it can send a notification to the sender (and admins if required) with custom text.
Worth checking out, if you haven't already: https://docs.microsoft.com/en-us/office365/securitycompliance/data-loss-prevention-policies
There isn't a quarantine feature but, there is a user override option, that might be worth looking at.