How to automatically rotate a monthly email

There are likely a few ways to do this. Here is one approach I can think of, using static lists to control the newsletter membership.

3 static lists

3 smart campaigns (batch campaigns all scheduled for the day of the month your newsletter goes out, assuming it goes out the same day each month.)

When a lead signs up for the newsletter, they get added to Static List 1.

Smart Campaign #1:

Smart list:

     Member of Static List 1

Flow:

     Send Email 1

     Remove from Static List 1

     Add to Static List 2

Smart Campaign #2:

Smart list:

     Member of Static List 2

Flow:

     Send Email 2

     Remove from Static List 2

     Add to Static List 3

Smart Campaign #3:

Smart list:

     Member of Static List 3

Flow:

     Send Email 3

     Remove from Static List 3

     Add to Static List 1 (if you would like the leads to keep rotating through the same 3 emails.)

If someone needs to be removed from receiving the newsletter for any reason, you could have a smart campaign listening for whatever activity designates removal, and the flow would just be to remove them from the static lists. To track engagement of the 3 emails separately with Marketo programs, you could have the above static lists and smart campaigns living in an "operational" Marketo program, and then a separate Marketo program for each email, with smart campaigns listening for when people open, click on, submit the form, etc. of each respective email (or whatever your Marketo program statuses are). Those smart campaigns would update the program statuses.

Hopefully this helped, and did not just confuse you