I have several domain and several domain emails. I am in an office with one other person. We share a cable internet connection through a router. If I send my co-worker an email from my domain email (email@example.com) to his email on the same domain (firstname.lastname@example.org) it goes direclty to his junk mail. If he sends himself an email (email@example.com to firstname.lastname@example.org) it goes direclty to email.
His junk mail filter is set at "low"
I have added "email@example.com" and "firstname.lastname@example.org" to his safe sender list
I have clicked on these emails in thejunnk mail folder and marked them as "not junk mail"
I don't know what to do next.