During the installation of the extension, the sql script sql/newsletter.sql fails, with this error.

ERROR 1171 at line 42: All parts of a PRIMARY KEY must be NOT NULL; If you need NULL in a key, use UNIQUE instead

Changing the definition of the version_status field in the ezxsubscription table creation instruction, fixes the problem

CREATE TABLE ezxsubscription (
id int(11) NOT NULL auto_increment,
version_status int(11) default '0',
subscriptionlist_id int(11) default '0',
...

becomes

CREATE TABLE ezxsubscription (
id int(11) NOT NULL auto_increment,
version_status int(11) NOT NULL default '0',
subscriptionlist_id int(11) default '0',
...