I can’t find the source, but I think this practice was mentioned in the recent Fulton County, Georgia indictment of former president Trump and his associates. It was also employed extensively by the now-disgraced General Petraeus to facilitate his extramarital affair [1]. It’s a pretty popular tactic used by people who aren’t very wise to the fact that their cleverness does not equate to actual privacy.
[1] https://www.cnet.com/news/privacy/petraeus-reportedly-used-d...