Yes it is!!!
Than...enter with root (admin password) and go to this path /var/qmail/alias that
contains alias files.
Example 1:
alias1@localdomain -> localuser@localdomain
I think that you may use this command: #echo localuser > .qmail-alias1
Example 2:
alias2@localdomain -> mike@yhaoo.com (external e-mail address)
#echo &mike@yhaoo.com > .qmail-alias2
I hope my samples are clear and useful.