Whitespace says an average of 100 MB free. For example DB1 had 80 GB of data. Moved all users but 1 with a 1 GB mailbox to another DB. No maintenance errors reported yet the whitespace script reports only 100 MB available for new mailboxes.

Are the disconnected mailboxes still present in the original store or have you purged them by turning the retention time down?

Do you mean that the value of the “AvailableNewMailboxSpace” field still show 100MB? How’s the value now, still the same? Please check the online defragmentation by using the counters in the article below, see if the task has been completed for the database Maintain Mailbox DatabasesPlease remember to click Mark as Answer on the post that helps you, and to click Unmark as Answer if a marked post does not actually answer your question. This can be beneficial to other community members reading the thread.