Create New-MailUser specifying DatabaseName and Custom Attribute 1?

Hello,

With PowerShell in Exchange 2010SP2, I'm trying to create a new user that is mail enabled in a specific Database and Custom Attribute 1 value.

I'm using this:

New-MailUser -Name "Firstname Lastname" -Alias firstinitiallastname -ExternalEmailAddress firstinitiallastname@domain.tld -FirstName Firstname -LastName Lastname -UserPrincipalName firstinitiallastname@domain.tld  -Database "MAILXXDB_DBNAME" -OrganizationalUnit "Domain.tld/OU" -DisplayName "Firstname Lastname" -CustomAttribute1 "My custom value" -Password (ConvertTo-SecureString -String 'Pa$$word1' -AsPlainText -Force)ResetPasswordOnNextLogon $True

but obviously this does not work as -Database and -CustomAttribute1 are not recognized parameters.

How can I specify Database and Custom Attribute 1?