Registering an account requires you to input your username/password.
{"msg":"Mail","action":"Register","username":"foo","password":"bar"}

If the account already exists:
{"MSG":"MailAccountExists"}

If the account doesn't exists:
{"MSG":"MailAccountCreated","Mail_Info":{"password":"fcde2b2edba56bf408601fb721fe9b5c338d10ee429ea04fae5511b68fbf8fb9","alias":"foo","folders":{"inbox":[],"sent":[],"spam":[],"trash":[]},"profile_image":"https://static.vecteezy.com/system/resources/previews/005/544/718/original/profile-icon-design-free-vector.jpg","signature":"","spammers":[],"blocked":[],"options":{"auto_reply":{"enabled":false,"reply_message":""},"_2FA":{"enabled":false,"secret":""}}}}