utilize mass_unsubscribe API call when removing ALL and/or subsets of members
xref Postorius issue #317 xref Mailman issue #998 (mailman#998) xref MailmanClient issue (mailmanclient#72)
Edited by Bryan Loniewski
xref Postorius issue #317 xref Mailman issue #998 (mailman#998) xref MailmanClient issue (mailmanclient#72)