We want to scan the contents of messages flowing between two parts of our organization, but when we tested screening products, they all interfered with mail transport. What's causing the problem?

Exchange 2000 Server supports all Internet-standard SMTP commands, but it also implements some Microsoft-specific command verbs that make data transfer between Exchange 2000 servers more efficient. Whenever you interpose a non­Exchange 2000 SMTP device between two Exchange 2000 servers, the device might filter out some of the verbs that Exchange depends on. For example, early versions of Cisco Systems' Cisco PIX Firewall were notorious for causing lines of "XXXXXXXXXXX" to appear in messages because of the way the software implemented SMTP filtering. In your case, the content-screening products are probably blocking the X-LINK2STATE and XEXCH50 verbs. The former verb transfers link state table information so that different servers can maintain a common routing table, and the latter verb efficiently transfers packets of 8-bit binary data.