c# Digital signature email through exchange server

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c# Visual Studio

Is it possible to send emails with a digital signature through an exchange server ?

I'm able to send emails with EWS Managed API 2.1 (Microsoft.Exchange.WebServices.Data; reference) in c# Visual Studio.

But know I want them to have a digital signature

This is my mail coding:

ExchangeService service = new ExchangeService(ExchangeVersion.Exchange2007_SP1);
service.Credentials = new NetworkCredential("user", "password", "domain");
service.Url = new Uri("https://exchangeserver.com/EWS/Exchange.asmx");

EmailMessage message = new EmailMessage(service);
          
message.Subject = "subject";
message.Body = "body";
message.ToRecipients.Add(sendto@something.com);
           
message.Attachments.AddFileAttachment(c:attached);

message.SendAndSaveCopy();