The action_mail_acct is not for sending audit alerts but for giving notifications about low disk space (below space_left or admin_space_left) when space_left_action or admin_space_left_action is configured to email. From auditd.conf(5):
space_left_action
This parameter tells the system what action to take when
the system has detected that it is starting to get low on
disk space. Valid values are ignore, syslog, rotate,
email, exec, suspend, single, and halt. If set to ignore,
the audit daemon does nothing. syslog means that it will
issue a warning to syslog. rotate will rotate logs,
losing the oldest to free up space. email means that it
will send a warning to the email account specified in
action_mail_acct as well as sending the message to syslog.
exec /path-to-script will execute the script. - -
admin_space_left_action
This parameter tells the system what action to take when
the system has detected that it is low on disk space.
Valid values are ignore, syslog, rotate, email, exec,
suspend, single, and halt. If set to ignore, the audit
daemon does nothing. syslog means that it will issue a
warning to syslog. rotate will rotate logs, losing the
oldest to free up space. email means that it will send a
warning to the email account specified in action_mail_acct
as well as sending the message to syslog. - -