Free tool / Bulk check
Every client’s email, on one page.
Paste the domains you look after. In under a minute you’ll know which ones Gmail and Outlook trust, which can be used for a fake invoice, and where to start.
Then fix them one by one
Start with “Delivered”
A domain whose forged invoice would be delivered has no DMARC policy that stops it. Open its report: the fix plan has the exact record, and where to click at its DNS host.
Hand over the plan
Each report can be emailed or saved as a PDF for whoever manages that domain, and the record builder merges several sending services into one SPF record.