This has already been requested and the idea / suggestion was turned down.
We as ISP hosts do require that some of our resellers have admin rights to their smartermail domains how ever resellers do find ways to abuse this features by creating additional mail accounts, deleting other admin accounts etc.

When users exist outside of web hosting control panels it prevents the control panel software that we use from being able to correctly report on usage.

Here is an example where a reseller has added in excess of 30 mailboxes.

I am requesting the smartermail consider adding features that allow us to restrict certain features for smartermail admins, in particular deleting and creating mailboxes.

Smartermail mail account count

SolidCP mail account count