qmail tried to deliver the mail, but there is no mailbox with that name. ezmlm-make(1) was used with incorrect arguments, often in conjunction with a virtual domain setup. If the list is in a virtual domain, the ‘host’ argument for ezmlm-make(1) should be the virtual domain, not the real host name. See What names can I use for my lists? and Lists in virtual domains for more info.
Other possibilities are that your qmail setup is incorrect. For a virtual domain controlled by user ‘virt’, create ~virt/.qmail-test containing ‘|/bin/echo "It worked"; exit 100’. Now send mail to ‘firstname.lastname@example.org’. If delivery works, you should get an error message ‘It worked’ back. If you get anything else, you need to adjust your qmail setup. Similarly, for a normal user, create ~user/.qmail-test and mail ‘user-test@host’ to test that you control extension addresses. If this fails, contact your system administrator or adjust your qmail setup.
If these tests worked, but your list still does not, you most likely supplied an incorrect ‘dot’ argument for ezmlm-manage(1). It should be ~virt/.qmail-test for the list ‘email@example.com’ and ~user/.qmail-test for the list ‘user-test@host’.