Final answer:
The sentence "Both Lee and I received the e-mail message that you sent us." is in the active voice because the subjects 'Both Lee and I' are performing the action of receiving the email.
Step-by-step explanation:
When determining whether a sentence is in the active or passive voice, you should look at what the subject of the sentence is doing. If the subject performs the action, the sentence is in the active voice. If the subject receives the action, it is in the passive voice.
In the sentence "Both Lee and I received the e-mail message that you sent us.", 'Both Lee and I' are the subjects, and they are receiving the action of 'the e-mail message' being sent. This might seem passive because the subjects are receiving the action, but the verb 'received' actually indicates that the subjects are performing the action of receiving the email, thus the sentence is in the active voice.