Use the below to export mailbox statistics from exchange PowerShell. There are different commands which help you filter and manipulate the exported data.
The exported information is always useful during Office 365 migration to assess mailbox sizes and item counts, last login time and required bandwidth.
Export Mailbox size and statistics of all users
get-mailbox -resultsize unlimited | get-mailboxstatistics | ft DisplayName,TotalItemSize,Itemcount | export-csv C:\temp\mailboxstatistics.csv
Export Mailbox statistics for a specific OU (organizational unit)
get-mailbox -OrganizationalUnit “OU=Sales,OU=London Staff,DC=contoso,DC=local” -resultsize unlimited | get-mailboxstatistics | ft DisplayName,TotalItemSize,Itemcount | export-csv C:\temp\salesstaffmbstats.csv
Export Mailbox statistics based on domain address
In this example we use the where cmdlet to specify the search filter base. In the below example I am searching for users with specific email address, useful in a multi tenant environment.
Here I am trying to export mailbox statistics for specific set of users who have exchangekb as their email address suffix.
get-mailbox | where {$_.EmailAddresses -like “*exchangekb*”} | get-mailboxstatistics | select-object displayname, totalitemsize, itemcount, lastlogontime, exchangeguid | export-csv C:\temp\exchangekbstats.csv
Exchange KB 