piped program in sendmail's /etc/aliases

If you're running a sendmail with smrsh set up (common in a lot of default configurations) you will need to run the piped command out of /etc/smrsh/. It can either be a symlink or a copy of the script, but if sendmail has 'smrsh' defined, it will need to be run from that directory. For example:

subscribe: | /etc/smrsh/parse-subscribe.pl

Check the sendmail documentation on smrsh for more details.

You need to quote the "alias" if it has a space in it:

subscribe: "| /home/icasimpan/parse-subscribe.pl"

or remove the space:

subscribe: |/home/icasimpan/parse-subscribe.pl