Hi. My company recently implemented an Exchange 2003 server. Most messages are sent and received fine. However, some messages to larger providers like AOL and Yahoo get delayed for a couple of days then fail altogether. I have verified that I am not on a SPAM blacklist. After looking around on Google I suspect the issue is related to reverse DNS. The domain name that supports our LAN is fake (it isn't registered). We do have a separate domain name for email that is registered. DNS hosted by our ISP points the real domain to our Exchange server. They also configured reverse DNS. We have an internal DNS server for hosts within our LAN. I have a couple of hints that could indicate what is going on. First, when I run nslookup on my Exchange server's public IP address is resolves as mail.realdomain.com. "mail" is not the host name of my mail server. Should I have my ISP correct this in DNS? Should I add a PTR in my internal reverse DNS for "mail" that points to the mail server? The second hint is in the delay and failure messages. A text attachment is sent with the delay message (with identifying info removed): Reporting-MTA: dns;mailserverhostname.fakedomain.com Final-Recipient: rfc822;user@xxxxxxx Action: delayed Status: 4.4.7 Will-Retry-Until: Sun, 22 Aug 2004 09:36:23 -0500 X-Display-Name: user@xxxxxxx Note that the Reporting-MTA: is pointing to the unregistered domain. This line of text is in the failure message: Could not deliver the message in the time limit specified. Please retry or contact your administrator. <mailserverhostname.fakedomain.com #4.4.7> Again the message referes to the fake domain. Google says #4.4.7 just means the message timed out. I'm sure this is easy one for you guys, but I am new to Exchange and DNS. Anys suggestions are greatly appreciated.