We are not receiving any external emails through our exchange server. Internal emails are received. Email was working fine until last night. The only change I know of is our ISP was supposed to setup reverse DNS. When some one sends a mail they receive a bounce back message:
Mail delivery failed: returning message to sender
A message that you sent could not be delivered to one or more of its recipients. This is a permanent error. The following address(es) failed:
The mail server could not deliver mail to email@example.com. The account or domain may not exist, they may be blacklisted, or missing the proper dns entries.
Windows SBS 2008 with exchange 2007
Thanks for you help.