Sending email in C# using office 365 using exchange API

See more:

C#

Office

API

Exchange-Server

mail

Hi Everybody,

I have a problem with sending email from my MVC application. Here is the code

ExchangeService service = new ExchangeService(ExchangeVersion.Exchange2010_SP1);
              service.UseDefaultCredentials = false;
              service.Credentials = new WebCredentials("EmailSender", "Password");
              string serviceUrl = "https://outlook.office365.com/ews/exchange.asmx";
              service.Url = new Uri(serviceUrl);
              EmailMessage emailMsg = new EmailMessage(service);
              emailMsg.From = currentUser.Email; //This email is different from Credential email
              emailMsg.Subject = mailSubject;
              emailMsg.Body = mailBody;

              emailMsg.SendAndSaveCopy();

The thing is that the Credential account is different from current user email. The users don't login in the domain so I have no access to their credential. So I want to use an account to send email instead of the users.It was possible to send email even without credential when we were using Exchange server but in office 365 I get this error:

The user account which was used to submit this request does not have the right to send mail on behalf of the specified sending account., Cannot submit message.

What I have tried:

The Credential user has 'Send As' access. maybe need on behalf access or something like that!?
Any idea?