Having really annoying issues with Exchange 2007. Before the migration on 2003, there were no issues with sending emails out of the server, and now getting the following emails bouncing back "randomly".
Undeliverable: (Email Subejct)
(Recicpient Name - randomnly from any server)
eg1. mailproxy1.pacific.net.au #500 Firewall Error ##
eg2. bay0-mc7-f1.bay0.hotmail.com #500 Firewall Error ##
eg3. bay0-mc4-f1.bay0.hotmail.com #500 Firewall Error ##
Server: Windows Serve 2003
Email: MS Exchange 2007
Hardware: Single DC/Mail Hub
Communication: SMTP 25 (inbound/outbound port is unrestricted on DC)
Email Clients: MS Outlook 2007
ISP Provider: Pacific Internet (Australia)
AntiSPAM: Enabled on Mail Hub
Send Connector: smtp.pacific.net.au
Firewall - Hardware: Cisco 1760 (unrestricted port forwarding 25 to Mail Hub)
Firewall - Software: Have been disabled during testing period on DC/Mail Hub and still occurs
Internet Conenct: 2 ADSL connections from the SAME ISP, although different conenction types (dont ask me why, this will be changed to 2 bonded conenctions in the future once I get this email issue resolved)
This issue seems absolutely random whereby clients can send out 10 emails to a single person and 3 of them bounce back. The average bounce back rate is approx 20% from what I can gather, and the majority of these issues had the errorstated above.
From what I can gatherthe majority seems to be public servers such as GMAIL and primarily HOTMAIL. I am believing that it could be the Exchange trying to handle all the outbound email and sending them directly without going through the proper mail host.
It was more apparent when I DID NOT configure smart host and channelled outbound emails via DNS, and it seems to have cut down the numbers as soon as smart host was enabled for out ISP.
There were other errors, which I do not believe have any relation to this particular type of errors.