After you call the sendmail binary, you can interrogate the $? variable for the exit code of sendmail. I am guessing that '0' means success, although the sendmail man page does not seem to list exit codes.

After your open using pipes or system call, or whatever you use to invoke sendmail:

# -- insert sendmail invocation here.
# eg. open(SENDMAIL, "|/usr/bin/sendmail -t")

$exit_value = $? >> 8;
$signal_num = $? & 127;
$dumped_code = $? & 128;
[download]

(from the Cookbook)

Anyway, how do you know that bounces are not the issue? Is the user who is sending the messages getting none at all? Maybe start off by checking the return values as above, but if sendmail is being run successfully and you are missing out on mails, I would look for bounce messages.

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