When I type the inside address of a letter, it is automatically double spaced. I have tried every suggested method of setting it to single line spacing and it doesn't change.
Use Shift + Enter to start a new line in the address
Modify the Paragraph formatting of the Envelope Address style so that there is no space either before or after the paragraph (and if 1 above does not work so that the line spacing in the paragraph is set to Single.
This is strictly a Word issue. The operating system has nothing to do with it.