[Threshold]

Or you can use just the one variable that you use to store the person who was the last to send a PM.

Example:

pawn Код:

// When a player receives a PM
if(LastPM[targetid] == INVALID_PLAYER_ID) SendClientMessage(targetid, -1, "You can use /r to quickly respond to PMs");
LastPM[targetid] = playerid; // playerid was the last to message targetid.

Reset LastPM[playerid] to INVALID_PLAYER_ID on OnPlayerConnect/Disconnect. Simple.