Both acs_mail_lite sendmail and smtp check the following prior to sending mail:
if { $valid_email_p || ![bouncing_email_p -email $rcpt] } {
To me (do not fully understand the whole bounce-stuff, what does bouncing mean, is this for addresses that send email back with an error message?) it seems that the current definition of the case-clause in query "can_send_p" for "bouncing_email_p" should be the other way round. The tcl-proc is called "bouncing_email_p", but the query is really doing a "can_send_p" so the logic in both does not match. Without the change, the system does not send any emails to users that have email_bouncing_p = "f" (which is the default)