R1:293a475e398b

Show why recipients were excluded from mail

Summary:
Ref T3306. This interface has a hard time balancing security/policy issues and I'm not sure what the best way forward is. Some possibilities:

# We just let you see everything from the web UI.
- This makes debugging easier.
- Anyone who can see this stuff can trivially take over any user's account with five seconds of work and no technical expertise (reset their password from the web UI, then go read the email and click the link).
# We let…