Powershell - Get-mailbox what's wrong in this statement?

$Item.Code_Site = "LO"

$JCAlias = (Get-Mailbox -RecipientTypeDetails sharedmailbox | Where-object {($_.CustomAttribute1 -eq $Item.Code_Site)}.Alias)

ERROR : The property Alias cannot be found on this object. Verify that the property exist....

Get-Mailbox has a property called alias..

so something is wrong in my statement.....

PS I I remove .alias  I get the name of the mailbox

$JC = Get-Mailbox -RecipientTypeDetails sharedmailbox | Where-object {($_.CustomAttribute1 -eq $Item.Code_Site)}

BUT this is not what I need....