I cannot understand why you don't offer the ability to suppress one list from another.
ie. - I want to send an email to our master list however I don't want some of the people to receive the email as they have already bought our service at a different price point. I uploaded a list of these people presuming I can simply select the master list to send to and then select my suppression list as 'do not send to these people'.
I have just been told I will need to copy our master list and manually delete the people I don't want the email to go to!!
This is not good practice.