using Gmail API using Service Account

I am trying to use the gmail apis for sending mail from a .net windows application. Can we use a service account instead of the user credential to call the apis? and does this require to use the googleauthorisationbroker to authorise? Delegating domain-wide authority to the service account – is this a mandatory step to be done while we use the service account? I have created a project and downloaded the key and copied to my applciation folder. The following code is written

//created google account credential from service account key and included the scopes
using (var stream = new FileStream("_**key.json**_", FileMode.Open, FileAccess.Read))
{
    credential = GoogleCredential.FromStream(stream).CreateScoped(Scopes);}
    //call the google api using the credential.
    var service = new GmailService(new BaseClientService.Initializer()
    {
          HttpClientInitializer = credential,
          ApplicationName = ApplicationName,
    });
    //send mail using the api
    service.Users.Messages.Send(message, mailaddress).Execute();
}

But i get the follwing error

Error = {Google.Apis.Requests.RequestError
Bad Request [400]
Errors [
	Message[Bad Request] Location[ - ] Reason[failedPrecondition] Domain[global]
]

---

I have also tried using user credntials codes also, it works but does nt work in some systems. No error as such is shown but the Authorisation page is not shown. Any thoughts on these issues?

[LindaLawton]

Service accounts will only work with Gsuite email accounts. The admin of the Gsuite (domain) account will have to grant the service account access to the users email account. Unfortunately i don’t have access to a Gsuite account so cant help you set it up. This might help Perform G Suite Domain-Wide Delegation of Authority

If this is a normal Gmail user account you are trying to access then you cant use a service account. You will either have to go though the SMTP / IMAP servers or using Oauth2 to authenticate the user.

[aluxnimm]

this is related to #987. now admin privileges are needed to open the listening socket at least in Windows 7 and 8.1.