Email address, first name, and last name fields are exported from Dynamics by default, so you are able to merge these fields into your email campaigns out of the box. If you wish to use other information which is stored within your CRM to customise your emails you will need to create a field mapping profile.
Field types which can be mapped include; single lines of text, option text, two options, whole numbers, multiple lines of text, and the date & time field.
There are field types which cannot be mapped. These include; images, floating point number fields, decimal numbers, currency, and lookup fields.