Mailboxes have been removed from a collection but they are still being displayed in the Statistics Portal and in the console.
The SQL database contains the statistics for the mailbox and the statistics continue to be displayed by the Statistics Collection Agent (SCA).
Statistics are retained in the SQL database for a mailbox. The retention period associated with the agents specifies the time the statistics will be retained. When the time has expired, the mailbox statistics are deleted from the SQL database.
The "Keep statistics for the last" X day(s)" for the Statistics Collection Agent (SCA) controls the time interval by which the statistics information will be kept and displayed regardless of the settings of the "Keep statistics for the last" X days" in any of the agents. For example if the Mail Target Agent (MTA) and Mail Source Agent (MSA) have the value set to 30 days and the SCA is set to five days, then the statistics will be displayed for five days after any change to the collection has been made such as removing a mailbox (statistics are no longer updated).
The lowest value that can be set in the SCA is one (1) day. Therefore to solve the problem above, reduce the "Keep statistics for the last" X day(s)" to one (1) day and the mailbox will be removed within 24 hours of its last update.
To set "Keep statistics for the last" X day(s)" for the SCA, select the SCA and Right Click on it. Select Properties. Select Logging and then set the "Keep statistics for the last" X day(s)" to the desired value.
Then stop and restart the SCA.