In your email mention that you are following up with your voicemail; that level of synergy, communication and integrity is sure to wow any professional and leave them with the impression you do what you say you’re going to do and you are organized.
Now before we jump into one possible solution, let’s cover an additional step you may want to add to your repertoire:

Remember that the speed of your words can negatively impact your message as well. "If you have to rush to get a message into the amount of time allotted for a voicemail message, you’re saying too much," DeCesare advises. "Say less and slow down. You want them to feel that talking to you will make their lives less stressful. If you're frantic and mumbling on the phone, it gives them a foreshadowing of what it will be like to work with you."
One quick way to sound more relaxed is to speak slower – slower than feels natural to you, even. If you rush the sales voicemail, it’ll sound like you’re trying to squeeze in your 50 calls for the day, and nobody wants to feel like they’re just another name on your list. Also, speaking slowly saves you from mumbling – if the contact can’t understand what you’re saying, what’s the point of learning how to leave a voicemail?