As a lot of clients are moving onto Office 365. As an Administrator, at some point you will need to check the Mailbox Usage for all mailboxes.
To obtain Mailbox Usage on Exchange Online. When you log onto the GUI, you will only be able to see the licenses assigned.
Then I checked the “Exchange Admin Center” > “Recipients” > “Mailboxes” > “Select the user ( Double click on the user)” > “Mailbox Usage”
There I found a Mailbox Usages report. Perhaps if you are looking for a few Mailboxes, this can do, however it is not scalable when
You have multiple users. Your best option would be Powershell. You first need to ensure you have the modules for Powershell
Click here: Assistance Connecting to Powershell
Once you log onto the Powershell Console, now you may begin. If you are an Exchange Admin like myself, this should be second nature as this is the same as connecting to a local Exchange server through the Management Shell.
To get a list of Mailboxes, run the following: Get-Mailbox
This will display the Mailboxes with the “ProhibitSendQuota”. For those who are not sure what this mean, it is the limit of when your Mailbox Usage reaches, you will not be able to send or receive emails.
Then run: Get-MailboxStatistics <Email address>
This will display the Users Mailbox, Itemcount and Lastlogontime
The itemCount will tell you how much of items are in the Mailbox, including deleted items, drafts, contacts calendar etc. combined.
Now run: Get-Mailboxstatistics -Identity <Emailaddress> | FL
The FL = Format list
This will now display all the Statistics Properties of the Mailbox.
The main attribute you may require obtaining the information is “TotalItemsize”.
To get a single users information, run the following: Get-MailboxStatistics -Identity <Emailaddress> | Select DisplayName,totalitemsize
Now when you run: Get-MailboxStatistics , it can only be run per user. How do you run it for the organization? You will need to combine Get-Mailbox with Get-MailboxStatistics
Get-Mailbox | Get-Mailboxstatistics | Select Displayname,TotalItemsize
When you run the Get-Mailbox (Pipe) means, I want a list of all the Mailboxes. Then Pipes is taking that information and what would you like to do with it. I want the Mailboxstatistics for each Mailbox. Pipe, I want all that information for all the Mailboxes, and now I would like to filter only for the following information: Displayname and TotalItemsize.
Therefore, this is what this Powershell line means: Get-Mailbox | Get-Mailboxstatistics | Select Displayname,TotalItemsize
CONCLUSION
From the GUI, you can get the Mailbox Usage, but it is per user base. To be more scalable, you will require to get the information through Powershell.