Journaling Effect on User Mailbox Servers

When journaling is enabled in a mailbox database and a user who has a mailbox on that mailbox database sends a message, the server generates two messages: one for the recipients and one for the journal recipient. When a message is submitted to a journalized mailbox database, the mailbox database processes the message as it typically would to deliver it, but it also creates a message for the journaling recipient. When a journalized mailbox database receives a message, most of the time, the message has been journalized already. In the receive case, extra processing (beyond reading the journaling property) is required only when the receiving server is the expansion server for the distribution list or when the distribution list is hidden or query-based.

Therefore, you can estimate the effect of journaling on a mailbox database by assuming that the enabled mailbox database can process approximately half of the messages being sent, as long as all other conditions, such as CPU power, bandwidth, storage space, and disk speed, remain constant.