To make sure that Word can find a column in your data file that corresponds to every address or greeting element, you may need to map the mail merge fields in Word to the columns in your data file.
To map the fields, click Match Fields in the Write & Insert Fields group of the Mailings tab.
The Match Fields dialog box opens.
The elements of an address and greeting are listed on the left. Column headings from your data file are listed on the right.
Word searches for the column that matches each element. In the illustration, Word automatically matched the data file's Surname column to Last Name. But Word was unable to match other elements. From this data file, for example, Word can't match First Name.
In the list on the right, you can select the column from your data file that matches the element on the left. In the illustration, the Name column now matches First Name. It's okay that Courtesy Title, Unique Identifier, and Middle Name aren't matched. Your mail merge document doesn't need to use every field. If you add a field that does not contain data from your data file, it will appear in the merged document as an empty placeholder — usually a blank line or a hidden field.