Thank you, Falko, for your response.
If Postfix works like Sendmail, does that mean that I can change Sendmail to Postfix and everything works fine?
I've tried that before. On my FC6 machine with Sendmail I've got a perl script with content as displayed below. After configuring smarthost in Postfix on my Debian machine I tried this same perl script after changing every instance of Sendmail in the cgi file to Postfix. I didn't really believe it would work, but if experts tell me Postfix behaves like Sendmail, I assume that scripts written for Sendmail work with Postscript. It didn't.
Below is a part of the cgi file where I changed every instance of sendmail to postfix (I didn't change it below and I tried the script also in its original form, but nothing worked):
# This email script generated by AutoCGIMail v1.2
# by Kristina Pfaff-Harris (http://www.tesol.net/scripts/)
# If you're having problems getting this to work, try putting
# $debugging = 1; on the next line.
$path_to_sendmail = "/usr/sbin/sendmail";
$email_field = "01Uw_e-mailadres";
$use_autoresponse = "Yes";
$autoresponse_message1 = "Geachte ";
$autoresponse_message2 = ",
But it's all not that simple. So how do I adapt things in such a way that my perl scripts, working well in Sendmail, keep on working in Postfix?
(Later this week I'll configure the apps again and try instructions at http://www.fredshack.com/docs/postfix.html