Yep. Andy and Mytoman have already given the import info. But since you asked, here are the actual rules for service:
06. Service
6.1 Service shall start with the ball resting freely on the open palm of the server's stationary free hand.
6.2 The server shall then project the ball near vertically upwards, without imparting spin, so that it rises as least 16 cm after leaving the palm of the free hand and then falls without touching anything before being struck.
6.3 As the ball is falling, the server shall strike it so that it touches first his court and then, passing directly over or around the net assembly touches the receiver's court. In doubles the ball shall touch successively the right half court of the server and receiver.
6.4 From the start of service until it is struck, the ball shall be above the level of the playing surface and behind the server's end line, and it shall not be hidden from the receiver by any part of the body or clothing of the server or his doubles partner.
6.5 It is the responsibility of the player to serve so that the umpire or the assistant umpire can see that he complies with the requirements for a good service.
6.5.1 If there is no Assistant Umpire, and the umpire is doubtful of the legality of a service he may, on the first occasion in a match, warn the server without awarding a point.
6.5.2 If subsequently in the match a service by that player or his doubles partner is of dubious legality, for same reason or for any other reason, the receiver shall score a point.
6.5.3 Whenever there is a clear failure to comply with the requirements for a good service, no warning shall be given and the receiver shall score a point.
6.5.4 Exceptionally, the umpire may relax the requirements for a good service where he is satisfied that compliance is prevented by physical disability.
6.6 If, in attempting to serve, a player fails to strike the ball while it is in play, his opponent will be awarded a point.
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And whether or not you can touch the table is determined by two different rules. And Mytoman correctly stated the meaning of those rules. The ball is in play when the toss is initiated. And when the ball is in play, you cannot touch the surface of the table with your free hand.
What Ma Long is doing is actually a very good way to start the serve. If you saw it from the side, you would see that most of his hand is off the table ensuring that the ball is behind the white line:
That isn't a great angle either but you can see that the ball is clearly behind the end line.
But the other reason that this is a great way to start your serve is that it ensures that you get low to start.
Sent from The Subterranean Workshop by Telepathy