I have TMO USA and can both send and receive MMS messages on 10iii with 4.5.0.19 using settings from XOXO’s post with the last octet correction of 145 in the proxy address.
I recall having to call T-Mobile and them having to do something to my account to reset it, but it was an easy thing they did, reboit my phone and it’s worked since.
I have had group text convos where many messages come in rapid succession. Sometimes I’ll have a few stuck in “downloading” stage and never receive them. Sometimes I have received them days or weeks later, which had led to occasional awkward or comical situations due to losing original context.
Overall, MMS and SMS operations are usable for me.