The IBM Lotus Domino server’s mail.box database is a busy place. It is constantly bombarded with mail routing activity. It is active when mail is received, when mail is delivered, and when mail is transferred — and it’s used by other Domino processes as well. Small and single-functioned as it is, it’s arguably the busiest application on almost every Domino server.

Every time a process wants to read or write mailbox data, it locks the database to protect that data from being corrupted or modified. The other tasks that are trying to work on the mailbox have to wait in line with their hands in their pockets and do nothing.

When the currently active process finishes what it is doing and unlocks the mailbox, the other tasks can have their turns and finish their jobs. Usually, these locks are only applied for a short time. But if a great deal of new mail arrives on a busy server that already has lots of mail traffic, or if someone sends a bunch of really large messages, there will be a lot of action, and the locking will be intense.

If a server has only a single mailbox, these locks might prevent the mail router from routing the mail efficiently. Mail slows down, and you know what happens next. It’s a phone call, exactly when you want to go to lunch.

Adding a second or third mailbox to a server can help alleviate this kind of pain. But how do you know when more than one mailbox is needed? I’ll explain what’s involved in figuring out the answer to this question and then show you how to make it easier to make the determination for multiple servers.