Your answer helped me A LOT!
The ONLY thing I changed from your set up was making the website http:// instead of https://.
I also found that sometimes it takes long to send a picture, so I turn off my mobile data and then turn it on again and it almost always sends the MMS after.
Honestly though, I probably won't be sending many MMS with this phone for obvious reasons, but as long as I can access the internet and download MMS, I'm good.
Thanks a lot for your help! 🙂