Not using Bamboo.LocalAdapter. Make sure you have
your mailer configured to use Bamboo.LocalAdapter or the
emails will not show up here.
You recently restarted your server. The viewer
does not persist emails so whenever you restart the server the list
will be cleared.
You're running multiple OS-level BEAM processes.
Sent emails are stored in memory. If you have more than one OS-level
process running, like "mix phx.server" in one terminal and "iex -S mix"
in another, emails sent in the latter won't be visible in the former.