I have a dedicated hosting box with a hosting company. People were complaining that they would try to send me an email and it would say user mailbox does not exist. My hosting company said they need to create a reverse PTR record for me. This seems to have fixed the problem for me but what about for my clients. If someone tries to send an email to someone@AnotherDomainOnMyHost.com won't they need their own reverse PTR record since when they do a reverse dns lookup it will say mail.MyDomain.com?