After installing and uninstalling AcyMailing Ver 8 (latest version), I followed the instructions to remove all tables. Immediately after dropping all tables, the website froze with a "missing acym_configuration table" error. I recreated the table using DDL from another site, and the error went away.
I turned on debug, dropped that table again, and got a trace pointing to JROOT/plugins/system/acymtriggers/ which had two files, acymtriggers.php & acymtriggers.xml
I renamed both files, dropped the #__acym_ configuration table again, and the system began operating normally.
I suspect these plugins should be part of the uninstall?