Microsoft is putting a "potential phising" warning on my mail ex KEAP

! “the actual sender of this message is different form the normal sender. click here to find out more”

this message is in the top of my mail ex keap… I see this in my test mail and I am deeply concerned that my clients will see this too… or that my mail will be diverted away from their in-box as it is seen as dubious in origin…

those receiving the mail are clients, have been active in Keap so its not that kind of thing…

Any advice / help to resolve this

thank you MARTINA