Change Exchange primary email address to lower case

By default Microsoft Exchange creates email addresses on the form First.Last@domain.com. If you change the email address policy to use lowercase, the existing email addresses are not updated to reflect that change.

It doesn't work to change the primary SMTP address to lower case right away, since email addresses are basically case insensitive. When you set a new primary SMTP address, the old address is kept as an alias email address. Exchange can't set a new primary email address since the same address already exists as an alias. More or less, you get the picture.

I created the following script to make the change

# Get all mailboxes in the users OU (select the OU for which you want to change to lower case
$Mailboxes = Get-Mailbox -OrganizationalUnit "OU=Users,DC=domain,DC=com" -ResultSize Unlimited
# Loop through all mailboxes
ForEach ($Mailbox in $Mailboxes)
{
    # Turn off email address policy
    Set-Mailbox -Identity $Mailbox.Identity -EmailAddressPolicyEnabled $false
    # Set a temporary primary email address
    Set-Mailbox -Identity $Mailbox.Identity -PrimarySmtpAddress "dummy@domain.com"
    # Remove the old primary address which is now a standard email address connected to the mailbox
    Set-Mailbox -Identity $Mailbox.Identity -EmailAddresses @{Remove=$Mailbox.PrimarySmtpAddress}
    # Convert the old primary address to lowercase
    $lowercasesmtp = $Mailbox.PrimarySmtpAddress.ToLower()
    # Set the lowercase email address as primary
    Set-Mailbox -Identity $Mailbox.Identity -PrimarySmtpAddress $lowercasesmtp
    # Remove the temp primary address
    Set-Mailbox -Identity $Mailbox.Identity -EmailAddresses @{Remove='dummy@domain.com'}
    # Turn on the address policy
    Set-Mailbox -Identity $Mailbox.Identity -EmailAddressPolicyEnabled $true
    # Check the result
    Get-Mailbox -Identity $Mailbox.Identity | select Name, *SMTP*, Email*
}