If your accounting and marketing team are using a mail provider that DKIM signs their emails that would be the most standard and widely adopted method I know of

If your accounting and marketing team are using a mail provider that DKIM signs their emails that would be the most standard and widely adopted method I know of. Each mail provider has different options for what to do with DKIM validation results but most will allow for quarantine, reject, put in a folder, or do nothing based on DKIM/SPF/DMARC results and based on the DMARC rules you create for your domains. LearnDMARC [1] was posted here recently and can show you how this is validated. [1] - https://www.learndmarc.com/ https://www.learndmarc.com/