Determining how many MAIL.BOX databases to place on a server

When a server sends and receives mail, server processes, such as the Router, access the server's MAIL.BOX database, writing messages to it and reading messages from it. Because only one process at a time can access MAIL.BOX, when mail traffic is heavy, access conflicts occur as multiple processes try to access the database simultaneously.

For servers that support a small number of users, access conflicts are rare, and the default of a single MAIL.BOX usually provides an acceptable level of service. However, on servers that support a higher numbers of users, creating an additional MAIL.BOX database can eliminate most access conflicts.

Table 1. Statistics

Statistic name



Total number of times that threads accessed any mailbox on the server.


The number of times that a thread attempting to access a mailbox had to wait because the number of concurrent threads exceeded the number of mailboxes configured.

For example, if there are three mailboxes configured, and there are four concurrent accesses, the conflict count would be incremented.

If the number of access conflicts consistently exceeds two percent of the value of Mail.Mailbox.Accesses, consider creating an additional mailbox.


The total number of current accesses (for example. a count of 2 would indicate that two threads are accessing mailbox at this time.


The number of times that the number of threads accessing the mailbox (that is, the value of Mail.Mailbox.CurrentAccesses) reached one less than the number of configured mailboxes.

For example, the warning count is incremented when two threads attempt to access MAIL.BOX concurrently and there are three mailboxes configured.

When the number of MAIL.BOX is 2, the value of Mail.Mailbox.AccessWarnings is always equal to the value of Mail.Mailbox.Accesses.

If you have more than three mailboxes configured, and if the number of warnings consistently exceeds ten percent of the value of Mail.Mailbox.Accesses, consider creating an additional mailbox.


The highest number of current accesses recorded.

By calculating the number of access conflicts as a percentage of total accesses, you can determine whether a server will benefit from the addition of another MAIL.BOX. In general, the number of access conflicts should be no more than two percent of the total number of accesses. However, because some access conflicts may result from unusually high peak loads, there's no need to eliminate all access conflicts. Only when the percentage of access conflicts remains consistently greater than 2 percent is an additional MAIL.BOX database warranted.

Note: Mailbox statistics are available only on servers where two or more MAIL.BOX databases are configured. You must restart the server to put into effect any changes to the number of mailboxes.