Redmine

I don't know if this is the expected behavior but I recognized that it's possible to reply to an issue of another project than the one specified in the /etc/aliases file.
Assume I have an /etc/aliases file with a line like this one:
foo: "| /opt/redmine/extra/mail_handler/rdm-mailhandler.rb --url=http://localhost:8080 --key=XXXX --project=foo --unknown-user=ignore"

Now I send an email to foo@someurl.net with subject "Re:[#123]" and 123 is the id of an issue that is not part of project foo, anyway the email is not refused.

I would expect that this should not be possible because I limited that emailadress to project foo.