[Lida]

Можно так:

public string SendEmail(string subj, string text, activityparty mailTo, activityparty mailFrom, Guid regardingid, string regardingType, string regardingName,CalloutUserContext userContext)
  {   
 try
   {
    CrmService service = setService(userContext);
    email Email = new email();
    Email.subject = subj;
    Email.description = text;
    Email.from = new activityparty[] {mailFrom};
    Email.to = new activityparty[] {mailTo};
    Email.regardingobjectid = new Lookup();
    Email.regardingobjectid.Value = regardingid;
    Email.regardingobjectid.type = regardingType;
    Email.regardingobjectid.name = regardingName;
    Guid emailId = service.Create(Email);
    // Get a TrackingToken
    GetTrackingTokenEmailRequest getTrackingToken = new 
     GetTrackingTokenEmailRequest();
    getTrackingToken.Subject = Email.subject;
    GetTrackingTokenEmailResponse getTrackingTokenResponse = (GetTrackingTokenEmailResponse)service.Execute(getTrackingToken);
    // Send the email
    SendEmailRequest request = new SendEmailRequest();
    request.EmailId = emailId;
    request.IssueSend = true;
    request.TrackingToken = getTrackingTokenResponse.TrackingToken;
    SendEmailResponse res = (SendEmailResponse)service.Execute(request);
   }
   catch (Exception ex)
   {
    return ex.Message;
   }
   return "";
  }
 
Вызывающая процедура (пример)
string sub = "subject";    
// To
    activityparty mailTo = new activityparty();
    mailTo.partyid = new Lookup();
    mailTo.partyid.type = EntityName.systemuser.ToString();
    mailTo.partyid.Value = SomeUserIdTo;
 //From
    activityparty mailFrom = new activityparty();
    mailFrom.partyid = new Lookup();
    mailFrom.partyid.type = EntityName.systemuser.ToString();
    mailFrom.partyid.Value = SomeUserIdFrom;
    string res = SendEmail(sub,description,mailTo,mailFrom, inc.incidentid.Value,EntityName.incident.ToString(),inc.title,userContext);