When I'm setting up the ReverseDNS for a server - for mail servers, is it acceptable for it to be the codename for the server? Or does it have to be mail.domain.tld? Like, say my server name was jack.... is jack.mydomain.tld acceptable? Or will it give me problems with MTAs on other hosts accepting my e-mails? It's not just hosting the mail server, but all services including web and MySQL.