I have a exim4 setup as SMTP. My user naming schema is to name all mail users for this server as m001, m002, m003, ... and then redirect to a real e-mail address with virtual domains. How can I allow my users to authenticate with exim to send mail using either their system user name (m001) or the email address ([email protected])? User login information for m001 are stored in linux system files (passwd, shadow). They are linked thru entries in a virtual address table for each domain that this server can serve: # /etc/exim4/virtual/example.com m001: [email protected] m002: [email protected] m003: [email protected] The same can be applied to qpopper ?