Mailbox count tool
Use the Mailbox count tool to determine number of mailboxes in your organization. It provides more information than Mailbox count on the Monitoring page. It is a command line tool. Download 32-bit or 64-bit Mailbox count tool, depending on your IBM Domino installation:
Run the tool with administrator privileges, or open a Windows Command Prompt (cmd) using Run as administrator. You can simply run the executable EMSL_VerifyMailboxCount_32.exe or EMSL_VerifyMailboxCount_64.exe to see the mailbox count.
If you need more detailed information, run the tool with one of the following parameters (options):
/names - displays extended information that includes user names, mailboxes and mail servers
/details - displays extended information and a list of Databases with their paths
/help - lists available options, you can also use /?