Our e-mail settings and docs were pretty out-of-date, and a bit

misleading. Some of the settings names had inconsistent capitalization,

and it wasn't always clear who would be receiving the e-mails. The

documentation was a bit worse, leaving out most of the settings and

improperly describing how to avoid suspicious e-mails.
This modernizes all this, renaming some of the settings for clarity and

consistency, and rewriting much of these docs to reflect modern behavior

and configuration for e-mail.

Built the docs. Checked for build, spelling, and link issues.