Facing the same problem realized that not only adding an accent character to the body solves it, but in any part of the json message sent, so you can add the "from" block with "name" and "address" read from get user api:

  "from": {
    "emailAddress": {
      "name": "the <displayName> field from get user api",
      "address": "the <mail> field from get user api"
    }
  }

I guess the "name" field should change the alias sender in the email received but it doesn't, does not matter what you put there it is always sent with original account display name, neither using block "sender", but it solves the encoding issue and the problem posted.

If anyone knows how to change the alias name please share!