We send a monthly email to our clients about our referral program. I have an email send program set to automatically send the email on a certain day/time each month. However, we have 3 different emails. I'd like to rotate the email that gets sent. For example, email #1 is sent in Feb., email #2 is sent in Mar., email #3 is sent in April, email #1 is sent in May, etc. What's the best way to do this?