Email Was Sent Twice to One Record
Issue
An email appears to have been sent twice to the same lead when it should not have been.
Solution
It appears that the record was sent the email twice because the record was merged with another record after the email was sent. So when the email was sent, the record was two separate records that was sent the email individually. This can be identified by looking at the record's activity log for a 'Merge People' activity