It would be good if there were a cross-client search function for email addresses in the frontend of campaign. Not only to search if the address exists, but also to see in which clients. If the search has found a hit, it should be possible to delete the recipient history from all existing or some clients. The search function should be dependent on the user rights and only display the clients to which the searcher has access. This function would save the support a lot of time and all deletion requests from customers can be invoiced.

The feature is requested for API lookup as well.