Be warned! If you have dupes in Marketo, communication limits are ignored. Just got this back from Marketo support when I contacted them about a larg chunk of my database gettiing 2 emails in a row:
Currently, Communication Limits in Marketo are set up on a lead basis, and not an email basis. If there are multiple leads in the database with the same email address, they will both be able to receive one email per day.