my G mail gets stuck in the outbox

[AC Question]

As I see I'm not the only one with this problem.
I have a Samsung Galaxy S 5 mini and I started experiencing the problem with gmail.
I have messages sending in my outbox for days, with and without attachments.

HELP

 

[Golfdriver97]

Welcome to the forums. Have you tried clearing the cache for Gmail in Settings>Apps>swipe over to all apps>scroll down to Gmail>click clear cache?