Does Qpopper support virtual domains?
Virtual domains are not currently supported by qpopper, but you can handle them by configuring your MTA (e.g., Sendmail) to map, say, joe@domain1 to user23, and joe@domain2 to user89 (or whatever). Then you tell Joe #1 that his email address is joe@domain1.x.y and his POP user name is user23, and Joe #2 that his email address is joe@domain2.x.y and his POP user name is user89.