They did not. The previous logo was the picture of an envelope plus the “M” letter written in red on top of it, which should obviously stand for “mail”. It was a brilliant idea already.

But what they did was to take the pallet of colors from the Chrome logo and spread it to other products they're as proud of as Chrome, in order to build a brand visual. Chrome is probably the most used software worldwide and across all softwares categories, so they'd better copy it for other products than do the other way around.

They got rid of the envelope because it is still there in the new “M” logo, only now it's suggested, just like the center square is in this picture: