Mailbox Item Count

Ever wondered how many items all the mailboxes in your Exchange environment currently have? Getting a weekly count of these, together with the total mailbox size, might be useful so you get a trend on your environment’s growth.
For a single mailbox, you can simply use the following cmdlet:

Get-MailboxStatistics user1 | Select ItemCount

Or if you want to get a count per database for example:

Get-MailboxStatistics –Database MDB1 | ForEach {$totalItems += $_.ItemCount}
$totalItems

If you want for every single mailbox in your environment, you can use the following cmdlet:

Get-Mailbox -ResultSize Unlimited | Get-MailboxStatistics | Select ItemCount | ForEach {$totalItems += $_.ItemCount}