I believe that there is a strong possibility that 2 Thessalonians 2:3 is speaking of the rapture. What do I mean? Some pretribulationists, like myself, think that the Greek noun apostasia, usually translated “apostasy,” is a reference to the rapture and should be translated “departure.” Thus, this passage would be saying that the day of the Lord will not come until the rapture comes before it. If apostasia is a reference to a physical departure, then 2 Thessalonians 2:3 is strong evidence for pretribulationism.
Ice, Thomas D., "The Rapture in 2 Thessalonians 2:3" (2009). Article Archives. 82.