Wondering if it is possible to see a history of emails that a GAE app has sent? Need to look into the history for debugging purposes.
Note that logging when I send the email or bcc'ing a user are not options for this particular question as the period I'm curious about was in the past (since then we are bcc'ing).
you can try one of the following way:
Log

write a log to datastore while each time you call sent_mail. 
write log with logging module and check the log in dashboard.

mail

while send the email, add a debug email address in email's "bcc" field. 
you can also check the "sent mail" in the email account used as sender.
Does a GAE app keep a log of the emails it sends?