Set up impersonation policy for internal domain, but was unable to do so for external recepient domain, where my Email and name is being impresonated and per O365 support there is no tool to do so. Does anyone know of a 3rd party email security tool or some IP tool to prevent &/or block such impersonation attempts of myself or my email or name or any user from my internal domain to external receptient domains?
I do not fully understand the question - you want to prevent spoofing?
In essence, as sender this isn't 100% possible as it always depends on the receiving end to perform authentication and verification of mail by sending host (SPF), domain keys (if applicable) etc. Only thing you can do is publish the proper information so receiving end can perform authentication and verification.