Centos 7, Webmin/Virtualmin up-to-date
:0
* ^From.*user@domain.tld
* !^FROM_DAEMON
* !^FROM_MAILER
* !^X-Loop: me@me.tld
| (formail -rt \
-A "X-Loop: me@me.tld" ; \
echo "Testing";\
echo "This is an automated response";\
echo "Not sure to see your message";\
echo "So please try again tomorrow" ) | $SENDMAIL -t -oi
An incoming mail from user@domain.tld to me@me.tld accomplishes the first condition and the automated response is sent to user@domain.tld but the original mail is lost, it is not delivered to $HOME/Maildir/cur as usual.
It is a long story of tests and log checks.
Summary: Postfix delivers incoming mail to Procmail. Procmail executes the recipe but does not deliver the original mail to inbox directory