GREAT PLANES RealFlight 7 User Manual page 97

Chat Messages (Received)-
This option allows you to modify the appearance of text you receive from
other players during multiplayer sessions.
These options function in the same way as the options for the Instructions
messages, except that they only affect Chat Messages (Received) messages.
There is one additional parameter available for this option called Play Sound.
This allows you to set whether or not a sound is heard when an incoming chat
messages arrives.
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