I recall an unclassified security briefing (mid 90’s) in which we were told all electronic communications in the world were monitored, thus the need to be very careful even when discussing items that were unclassified standing alone. At that time it appeared that friendly countries were playing quite a game - the US wouldn’t spy on itself in violation of the law, they’d let someone else do it with the implicit agreement that if anything dangerous showed up, the US would be given sufficient information to act. Likewise with say, just a wild guess, the British.
From the Starr report:
“According to Ms. Lewinsky, she and the President had a
lengthy conversation that day. He told her that he suspected that a foreign embassy (he did not specify which one) was tapping his telephones, and he proposed cover stories. If ever questioned, she should say that the two of them were just friends. If anyone ever asked about their phone sex, she should say that they knew their calls were being monitored all along,and the phone sex was just a put-on.456