I think it would be good practice to not use the administrator as a common board user, but only for board configuration. That means that I wouldn't regularly log in with the administrator account, and therefore wouldn't notice PM-s.
On my boards, the administrator is like root: necessary for administration, but not on the board as a user. Instead, there's a user account with moderator permissions for the "administrator" of the board. I want my people to contact that user, instead of the big administrator account. Therefore, I wouldn't want to list the administrator, ever.