A web applications sends two emails:

1. to the user of the webapp
2. to the administrator

the administrators mailbox (qmail) is on the same machine as the web application (php, apache, /usr/sbin/sendmail).

email 1 works, email 2 sometimes doesn't work. I don't see any pattern in the mails that don't work. Also because I don't exactly know WHICH emails failed (since the email itself would be the only notification).

email 2 looks like this:

from: <[email protected]> #changes for each user
to: <[email protected]>

What could be the problem?

Are rejected emails stored somewhere? (if they are rejected.. how do I check this?)