Your check was not put in the envelope.
Active voice tends to give writing a less wordy, more direct and lively effect.
It takes more words to use passive voice. Passive voice can also result in excessive wordiness or create vagueness. It has been learned that. . Generally, it is best to use the active voice, but in some cases, the passive voice is appropriate and possibly even more effective than the active voice. When the performer of the action is either unknown or of less emphasis in that sentence than the receiver of the action, the passive voice is effective.