How can I see a log of emails that Drupal has sent?
Drupal doesn't keep hold of that information, so your server mail logs are the place to look.

Some email operations are recorded to the watchdog, but not all. You can get a look at a few of those ops with a simple query like this

SELECT * FROM watchdog WHERE message LIKE '%email%'


That'll get you false positives, but also should show you what operations are actually recorded (welcome message sent, new password sent, etc.).

For future reference, you can use either of these modules to log outgoing mail:


Mail Log
Email Log