LINUX POP3 Authenitication problems

When I set up new users on our POP3 server, the new user logons are unable to authenticate. PAssword is deemed as incorrect even though I am using the one I created. I am using the following command string to create the new users: useradd [username] -s /bin/false -p [password] I then add the users to the virtusertable and execute the “make” command to compile. What am I doing wrong? Is there a way to change the passwords?