Below is a list of interesting points and concepts regarding the Microsoft Exchange Server message transfer agent (MTA).

• Function of MTA database (.dat) files and their deletion
  The MTA needs a core database in order to function correctly. A copy of these core .dat files are found on the Exchange Server compact disk, in the Setup\platform\Bootenv folder. These same files are also found with other MTA files on the compact disk in the Setup\platform\Mtadata folder, but it is easier to discuss and use these data files if you see them isolated in one place.
  In the Bootenv folder, you see the files Db000001.dat through Db000026.dat. These file names are ordered in hexadecimal values, so there are actually 39 .dat files, including the Dbbitmp.dat file. Additional data files are created as needed by the MTA as it transfers data between systems and components. Modifying or replacing any .dat files is not recommended unless this is suggested by a Microsoft Support Professional.
  When the MTA service starts, it checks for a placeholder file (Dbbitmp.dat) to see if the service last stopped without an error. If the file is missing, the MTA runs an internal MTACHECK to verify database integrity. In Exchange Server 4.0 and 5.0, the command-line version of MTACHECK does not create this placeholder file and therefore, the MTA assumes the MTA database needs to be checked.
  You also see a file called Oxzboot.env in this folder, which is a textual representation of the database boot environment for the MTA.
• The reason behind Exchange Server MTA continuing to route outgoing SMTP mail to the Internet Mail Service, even though it is not currently functioning.
  The Exchange Server 5.5 (and earlier versions) MTA does not check the state of the next link as part of the routing calculations.
• The type of connector to be used in connecting Exchange Server sites in an organisation.
  It depends on bandwidth and other considerations. For additional information, click the article number below to view the article in the Microsoft Knowledge Base: 190022 XCON: Comparison of X.400 and Site Connectors
• What size restriction to put on Exchange Server MTAs or connectors.
  That depends on how important speedy mail delivery is to your organisation. The Exchange Server MTA has become quite robust over the past few years; however, if a user sends a 100-megabyte file in an e-mail message to 10 users on 10 different servers, it will take some time to process this mail depending on server hardware, available bandwidth, and so on. During this time, delivery of other user mail may be delayed.
• A user sends a message to the entire global address list. Many other users select Reply All, and send it again. These replies are generating a flood of e-mail, causing mail delivery to be extremely slow across the organisation. How to remedy this and prevent it from happening in the future?
  This situation is called "bedlam." To remedy the situation, search the TechNet CD for "bedlam." Locate the document that is titled "Preventing and Correcting Large Distribution List Message Storms," which contains information on cleaning up bedlam situations and on restricting access to distribution lists (DLs).
  You can also limit the number of recipients on the To line of a message in order to prevent a message storm. For additional information, click the article number below to view the article in the Microsoft Knowledge Base: 126497 XADM: Limiting the Number of Recipients of a Message
• On the Stack tab of the X.400 Connector Properties page, the preferred option of Remote host name or IP address option for the remote server
  Although either option works (depending on the name resolution methods used), using the IP address is the preferred option. There are fewer problems with name resolution when you use an IP address at each end of the connector. If you use the Remote host name option, you can use the NetBIOS name, or Fully Qualified Domain Name (FQDN).
  However, Microsoft Product Support Services (PSS) has found that for the most reliable, trouble-free Exchange Server environment, the best option is IP address; type the IP address of the remote server in the Address box on this property page.