I have a few question concerning DNS, ,and exchange 2003. Users on my network send an email message to colleague's who have valid email accounts sometimes the email comes back right away, and something its weeks before they get an error like the one below.
"The e-mail system was unable to deliver the message, but did not report a specific reason. Check the address and try again. If it still fails, contact your system administrator.
<xxx.xxx.com#4.0.0 smtp;451 <email@example.com>... Requested mail action not taken: mailbox unavailable>"
Also what are the benefits of using reverse DNS? and should I be using it?
Also has anyone run into a problem with the greylisting?
Any information would bee greatly appreciated.