I just tested this with my Droid Maxx and the stock keyboard. It did not insert a space before the "@". Is this happening to you after certain typed phrases? I know that the keyboard does some predictive replacements - maybe this particular phrase is in your on-board dictionary?
You can check the personal dictionary. From home, settings, language and input. Tap the control icon next to "Google keyboard", it's the first entry under "TEXT CORRECTION". If you have something in there that you don't want, you can remove it. Or, if it's not that, maybe it's the auto-correction; try setting that to "none" and see if the problem goes away. Or, if it's not that, under "Advanced settings", try turning off "Suggest contact names".
(FWIW, I use Swiftkey myself, and that stupid space after the period and before something like "com" keeps happening in almost every app. Swiftkey does sometimes sense that you are typing a URL or email address and will not do the replacement, but if I am trying to type somebody's email address in the body of a mail message, it's always period, backspace, com. It drives me crazy; I'm quite happy hitting the space myself when I want it. Too bad the stock keyboard isn't better.)