Can't send mms with Hangouts I have a Galaxy Note 4, running Android 6.0.1 and I can't send MMS with Hangouts. I can receive and send MMS with the stock SMS app, but only receive MMS with Hangouts and I can't find whats is going wrong because it worked perfeclty fine before.

Hangouts is my default SMS app.

I deinstalled/reinstalled Hangouts, no changes.

I can sens MMS with other apps, I tried Textra, but now my battery drains really fast.
On many devices, messaging apps (even those with full access to SMS) are unable to send MMS messages unless they are set as the default SMS app. 

This same issue affects to me on my Nexus 6P: my default SMS app is the Messenger app, and even though other messaging apps on my phone (Textra and Pulse) have access to SMS &amp; MMS, neither can send MMS without being set as the default SMS app in Settings. Both of those apps prompt me to set them as the default SMS app when attempting to send MMS, I'm surprised that Hangouts does not.

So, to fix the issue: go to Settings -> Apps -> gear icon in the top-left -> SMS app -> Hangouts. Or, alternatively, search through Settings for "Default apps" or "SMS app".

tl;dr: Setting Hangouts as your default SMS app will fix the issue.