Galaxy S6 - MMS gifs not sending?
I figured out how to send .gif files with my Samsung Galaxy S6 Edge and I'm sure there are others out there that are just as frustrated in their search. I tried downloading several .gif editors like Textra and they just did not work the way I wanted. The one app that I found that works is Google Messenger.

Steps I did that worked:

Downloaded Google Messenger app (free from Google Play Store), use Google Messenger as your default texting software for your device (MMS), google a .gif file you want to send (DO NOT TRY AND SAVE IT FROM THE GOOGLE THUMBNAIL PAGE.  CLICK ON THE LINK TO THE ACTUAL WEBSITE THAT HAS THE GIF ON IT), hard press the moving .gif to save to your phone, open GOOGLE MESSENGER, attach the .gif file to a text message from your gallery (IT SHOULD SHOW AS MOVING ONCE YOU HAVE ATTACHED IT), and hit send!! I hope it helps. Good luck!!!