We do not host our email. We have an ISP that hosts it. We send mail through another ISP.
But we do have an exchange server that is giving some of my users the smtp; 550 5.1.8 error sender IP must hae reverse dns (DNS PTR) for 18.104.22.168.
This does not happen to everyone.
If I as administrator send mail to same area everythng goes aok. If I send via webmail under the user getting the error it goes aok. Only if send via my exchange server our to our EMAIL ISP.