I am trying to understand the mailbox size.

[fedoracore]

I am trying to understand the mailbox size. We have a on prem Exchange server. Please see the picture below, why is there discrepancy between what is shown on Outlook client and the Exchange server itself . Left side is the Outlook client, the right side is Exchange server one. 

[#2 · Accepted solution]

@fedoracore What you see on ECP, whatever version of Exchange or Exchange online if you are using includes all data in IPM except Recoverable items ( deleted items in this case ) whch is shared across your IPM and non-ipm data folders.

IPM contains the default front end folders like inbox, sent items drafts , etc and deleted items (partially) , when an item is deleted from deleted items and it moves to recoverable items folder (Last chance) it moves into NON-ipm which is separate from Mailbox regular statistics and hence displays the same on ECP/Admin Center which is different from your Outlook statistics.

For Best results, always run below command to fetch statistics which will give you exact data a mailbox is consuming Technically from backend mailbox database.

Get-MailboxStatistics user@domain.com | FL 

Also for getting information about each specific folder and how much data your recoverable items folders are consuming - 

Get-MailboxFolderStatistics user@domain.com | Select Name , Foldersize , Itemsinfolder

For specific to Recoverable items run below - 

Get-MailboxFolderStatistics user@domain.com -FolderScope Recoverableitems | Select Name , Foldersize , Itemsinfolder

https://docs.microsoft.com/en-us/exchange/policy-and-compliance/recoverable-items-folder/clean-up-de...

https://docs.microsoft.com/en-us/exchange/security-and-compliance/recoverable-items-folder/recoverab...

https://docs.microsoft.com/en-us/exchange/policy-and-compliance/recoverable-items-folder/recoverable...

Cheers !!

Ankit Shukla

[#3]

Thanks Ankit!!

[#4]

I'm glad it resolved the issue as well as explained the issue for which you were looking for answer. Please mark as answer of that resolved your issue.

[#5]

Actually looks like there is something else. I did not articulate it well