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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