Multiplayer contrails

Hello all,just yesterday a had a long haul flight from Europe to Canada on Vatsim using SquawkBox4 in FSX. One thing I was looking forward to was the FSX feature (at least I read somewhere about it) of it showing contrails at multiplayers' planes at high altitudes.Well, I had several in-flight encounters, with other players coming close as 2 nautical miles range within my own aircraft. Unfortunately, none of them had any contrails. The airplanes were displayed correctly, there was just no white tell-tale behind them.Is there any setting I might have forgotten to "activate" in order to have them in multiplayer?Thanks for any advice!Best wishes,Rafael