This usually happens when you're using an off network phone. i.e. an AT&T phone on T-Mobile, or low-cost carrier with a branded phone.
The solution is usually to manually edit the APN with the correct information. For Windows 10 mobile, go to Settings-> Network & Wireless -> Cellular & SIM -> SIM Settings
Be sure your Cellular connection profile is set to the correct provider, then add the correct MMS APN. Of course, you'd have to look up the correct settings on your provider's website.
09-21-2017 12:32 AM