We have SBS2008, which was migrated from SBS2003 and working fine for about a year. Outlook 2007 is the client and OWA has the same results. Recently, we are sending e-mail to some domains and they are not receiving them - most domains work fine. We are using our ISP as the Smart Host on Exchange, but even when we change to DNS, the e-mail doesn't get there. I've turned on logging and the logs show that the e-mail was sent. There is nothing in the SMTP queue.
We are not showing up on any blacklists.
We are also using GFI to add a disclaimer to the end of every e-mail.
What tools can I use to troubleshoot this?