I’m looking for a way to verify the sender of an email by the recipient that is easy use by non-technical users and is cross platform.
Using something like GPG email signing is not something I can ask our accounting or marketing team to reliably and securely do on their own (especially when everyone is working remotely).
LearnDMARC [1] was posted here recently and can show you how this is validated.
[1] - https://www.learndmarc.com/