I was trying to upgrade vpopmail from vpopmail-5.4.13 to vpopmail-5.4.16. And notice that qmailadmin-1.2.1-r1 won't work normal (can't edit records) with current vpopmail-5.4.16. Writes something like internal error on server. Rollback to vpopmail-5.4.13 helped.
Problem appear when you are making emerge net-mail/qmailadmin-1.2.1-r1 after installing net-mail/vpopmail-5.4.16. It can be fixed if you install net-mail/vpopmail-5.4.13 then net-mail/qmailadmin-1.2.1-r1 and after that you can upgrade to net-mail/vpopmail-5.4.16.
please try with vpopmail-5.4.19 and latest qmailadmin and reopen if this doesn't fix your issues.