Complicated mail merge

I have a mail merge situation I’m trying to resolve. I understand using IF..then..else conditions but I believe this may go one step further.

I have 4 different scenarios in my source data. If it’s scenario 1, it will get letter 1. Scenario 2 will get letter #2. Scenario 3 will get letter #3. Simple so far…here’s the part I don’t know how to do. Scenario 4 – there are some records that contain two email addresses for the record in the data source. In this situation I need to send letters 3 AND 4. How do I tell it to send two emails to two separate email addresses that are contained in one record in the data source?