Reply To: Automatically insert space during typing

You can do this with paragraph styles as a grep style.
You’ll need to create a character style with the “no break” setting.
Then in the paragraph style options under the GREP Styles add a New GREP Style
In the Apply Style: field you will select the “no break” character style. In the To Text: field you will put (?=\.\.)
This will create a nonbreaking space at every space followed by two periods.