[sqwebmail] mail delivery problems?

[David Liu]

in the past 12+ months we've had the following mail delivery problems with 
sqwebmail/courier

1. sometimes, sending an email doesn't actually get delivered. it just 
"disappears"
2. if an email bounces for whatever reason, re-attempts (and thus more 
bounces) occur every month or so

any ideas to what's happening and what i can take a look at?

thanks

dave