A mailmerge can only have one data source in the sense that it is usually
understood within Word Mailmerge.

However,
a. that data source can be a view, which uses a join to bring together
related data from multiple tables and views. as long as there is something
to link each recipient with the appropriate return address you should be
able to combine the two sets of information in a view
b. if you aren't allowed to create a view in your database, you can issue
the equivalent SELECT statement from Word VBA. However, your query is
limited to around 255 or 511 characters, and that can be a significant
limitation
c. you can sometimes insert pieces of information that come from other
sources of data using DATABASE fields. However, before going down that route
you should really try out (a). If you're not familiar with SQL and views,
tell us a little bit about the structure of the tables you need to get the
data from and maybe we'll be able to make some suggestions, or you could try
asking in a more SQL-related group.

Peter Jamieson