How does the MTA work?
One of the key elements to understanding how to troubleshoot and maintain the SMTP MTA is understanding its basic operation. How does it send messages? How does it receive them?

The SMTP MTA consists of several distinct tasks and requires several Notes databases for its operation. Following is a description of the database files required:

• Mail.box is affectionately known as "mail dot box". In any case, mail.box is the mail router database. Any mail routed to the Domino server uses mail.box as a temporary storage until the mail message is either transmitted to another server or into the user's mail database. Mail.box is not technically part of the SMTP MTA, but is used by Domino mail routing.

• Smtp.box is a mail routing database specific to the SMTP MTA.

• Smtpibwq.nsf is considerably harder to pronounce than mail.box. The wonderfully descriptive sequence SMTPIBWQ stands for the SMTP MTA InBound Work Queue database [like they couldn't just call it in.box? -- DG]. Messages being received are temporarily stored in this database until they are converted into Notes format and routed into the Domino server environment.

• Smtpobwq.nsf is nearly as unpronounceable as it's twin. In this case, the file name stands for SMTP MTA OutBound Work Queue database. Messages being sent are held in this database until they are successfully transmitted to the Internet.

These databases are used by several SMTP MTA tasks. A somewhat condensed description of the operation of the SMTP MTA goes like this:

A user within your Domino environment sends a message to the Internet address: jon@msphub.com. The Domino server accepts the message and places it in the mail.box database. From there it is routed to the Domino server where the SMTP MTA is running, and then it's placed into the smtp.box database.

The outbound message conversion task of the SMTP MTA continually polls smtp.box for new outgoing messages. As new messages are found, the message conversion task converts the message to SMTP format; file attachments are converted to MIME. The message is then deposited in the outbound work queue database in native Internet mail format.