The Mailzu summary does a mysql query error.
I've see the logs and the error was in the following query:
mysql> SELECT msgs.content, msgrcpt.rs FROM msgs INNER JOIN msgrcpt ON msgs.mail_id=msgrcpt.mail_id LEFT JOIN maddr AS recip ON msgrcpt.rid=recip.id WHERE AND NOT (msgs.quar_type = '') AND (msgrcpt.rs='' OR msgrcpt.rs='v' OR msgrcpt.rs='p');
ERROR 1064 (42000): You have an error in...
2007-02-12 11:37:07 UTC in MailZu