Struggling with e-mail overload? Google (GOOG -1.3%) is hoping a big Gmail overhaul will address the problem. The update, which will gradually roll out to both PC and mobile users, splits the traditional inbox into 5 categories - Primary, Social, Updates, Promotions, and Forums. Messages can be moved between categories, and e-mails from a particular sender can be set to appear in a particular category. Gmail was estimated by comScore to have nearly 300M monthly users last fall, and is still gaining share. However, Microsoft and Yahoo both recently overhauled their e-mail offerings in an attempt to keep pace.