Query on service rules under 21-point system

[iMakk]

Just wanted to understand rules pertaining to the galleries while serving in a doubles game.
1. The back-gallery used to be 'out-side of play' for serving under the 15-point system but want to check the latest rules. Saw some matches some time back where the back-gallery was included in the serving area and the players were using the high-serve. We are trying to move from the 15-point system to the 21-point system where I play and there is lot of confusion around this.
2. If the back-gallery is included in the serving area, what about side galleries?
Thanks for the help in advance.

[kwun]

receiving area remains unchanged. has been that way for decades.