A family of Microsoft word processing software products for creating web, email, and print documents.
The explanation is likely one or more of the Pagination options (on the Line and Page Breaks tab of the Paragraph dialog box) which are enabled by default for text paragraphs in Word.
For example, widow/orphan control prevents a single line of a text paragraph from being left "alone" at the top or bottom of a page. You can turn off all of these options which may make a difference.
However, the best fix will depend on what you are dealing with, exactly. For example, is there a blank paragraph between the end of the message and the greeting? Or is the vertical space created with Spacing After (or Spacing Before)? On the Home tab, click the ¶ icon to find out more. Paragraph marks are represented by pilcrows, ¶.
See also Suzanne S. Barnhill's article at http://wordfaqs.ssbarnhill.com/BottomLine.htm .