Hello Satis,
Unfortunately, there is no easy way to delete messages for inactive users through the program. In fact the method you mentioned is the only way to do it. Please contact support, we will be able to run a script for you that will delete the unwanted messages.
In the meantime there is a preference you can turn on that will automatically clear the "Deleted Messages" box when logging out.
On the main screen of AC, go to Edit -> My preferences -> User Preferences.
In the Messages section check off the box for "Automatically clear "Deleted Messages" box when logging out."
![[Linked Image from ]](/ub/attachments/usergals/2012/12/full-3500-427-delete02.jpg)
This is not a practice wide setting and will have to be done for each user.
It should help keep those message numbers down to a manageable level.
Thank you for your continued support,
Craig@AC