Question:
I would like to know what report can give me the top 10 largest mailboxes in the organisation.

Answer:
The report template you are looking for is called Mailbox Storage Information and you will find it on the Templates > Storage menu. Information is dynamically collected through via PowerShell (from Exchange 2010 onwards) or a dynamic MAPI connection to Exchange (Exchange 2007).

You will apply the following settings:

• Selection tab: All organization mailboxes.
• Group tab: No grouping.
• Filter tab: N/A.
• Options tab: As shown below.

• Content tab: Set the detail level to Mailbox storage (item size and count).
• Presentation tab: Display = Table (for a table only), Graph (for a graph only), Graph & Table (for both), Size in MB = MegaBytes.
• Output tab: Your own choice (Screen, Printer, Disk file, Email recipient, Sharepoint, Database table).

See also:

• How do I obtain a list of my mailboxes' sizes?
• How do I obtain a report showing users who have exceeded their quota?
• How can I send a message to all mailboxes over a certain size?