And of course it's all just JMAP under the hood!

["MaskedEmail/set", { "create" : { "k1" : { "state" : "enabled", "description" : "Hacker News", "url" : "https://news.ycombinator.com" } } }, "R1"]

returns:

["MaskedEmail/set", { "created" : { "k1" : { "id" : "masked-123456", "email" : "flighty.emu5803@mydomain.example", "createdAt" : "2021-09-28T14:19:19Z" } } }, "R1"]

Very simple to work with.