Hello Salem, 

Thanks for reaching out to the community. Please keep in mind that the disk usage includes calendar items, Notes, File storage, team workspaces, etc. 

Please let me know if this helps. 

Kind Regards, 

Hello Salem, 

I would start by verifying where the disk space is being used ( Like Zach mentioned above ), is this all Email or does it include File Storage, etc. 

Select the mail tab -> Than the info circle at the bottom next to the size, it will show where this is being used. 

Once this has been verified that the usage is in the mailbox you can move on. IN outlook are you seeing any "Sync Issues" that may indicate that all the messages are not being downloaded? Are you using compression on the Archive file? 

You can try and import the archive into a test user and see if the message count is correct for the folders.

Thank you

Tony

Hello Tony and Zach,

thanks for replying.

We are using smartermail 12.5. 

When I check user's disk usage it shows x GB for sent item and y GB for inbox. the total is assumed Z.

When we use IMAP and sync his mail to ost file, all MSGs are sync and number of inbox and sent item is the same in outlook and smartermail, but Z (size) is different. Smartermail is reporting 3 times more! 

Is it possible for you to check the same scenario in your lab or home?

I checked it for different accounts including mine on the same mail server. For example, smartermail repors 600MB usage for me, but when I sync it with outlook it decreases to 250MB. 

Confusing! 

Is there any why to make sure if everything is okay? A user with more than 2000 mails can't check them all before making a backup to a file and then removing mails from the server.