Enhance: flagging emails as spam to exclude them from view

Spam e-mails are a nuisance; they get in the way when browsing lists. It would be helpful if they could be ignored when displaying emails to a list.

So I suggest that there should be a way to flag e-mails as spam, and the user should be able to suppress the display of such messages.

There would need to be some controls on who was allowed to flag the messages.
Rather than a binary flag, users could select to suppress messages with a spam vote > N

No files, tests, or entry points are identified. Start by locating the email-list display, message metadata, and permission handling; done means users can flag messages, configure suppression by vote threshold, and apply defined authorization controls.

Written by the indexing model from the issue text.