This plugin adds "mark as spam" or "mark as not spam" button to the message
menu.  When not in the Junk mailbox, messages are moved into the Junk mailbox
and marked as read.  When in the Junk mailbox, the buttons are changed to "mark
as not spam" or "this message is not spam" and the message is moved to the
Inbox.  The learning driver allows you to perform additional processing on each
message marked as spam/ham.

WWW: https://github.com/JohnDoh/Roundcube-Plugin-Mark-as-Junk-2