Virtual domain users need to use the following format for thier user name when popping in:
user%virtual_domain_name

Eudora might require the following syntax:
user%virtual_domain_name@pophost

Microsoft clients may take the following syntax:
user@virtual_domain

If you don’t include the %virtual_domain_name, vpopmail will assume it is either a /etc/passwd user or a vpop user in ~vpopmail/users or configured with “default domain”.