I've found I can decrease confusion a little by using from.{their company name}@mydomain.com and when I care about making it more phish-proof, I can go for

I've found I can decrease confusion a little by using from.{their company name}@mydomain.com and when I care about making it more phish-proof, I can go for e.g. from.{their company name}.{some numbers}@mydomain.com