Have had sent emails stuck in gmail outbox with Android for years. Have tried all suggested fixes no help. I’ve tried it all and gmail stinks. There is nothing but the same community help know it alls who suggest the same “simple” fixes, connection, clearing caches and cookies, restart gmail app, blah blah. Google Gmail has known of this pathetic issue for nearly 10 years and only leaves it to the community to resolve. Guarantee you i will not buy another android pos