When I first Upgraded to W10M my MMS settings didn't come over and I had to set them manually...
Use this site to find your country and carrier then use the values they provide:
World Wide Mobile Phone Settings Or check the help pages at your Carrier's website.
W10M: Settings > Network & Wireless > Cellular & SIM > SIM settings > Add an MMS APN > enter the values > make sure the "Apply this profile" box is checked > tap Save.
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