Ошибка : threw exception:
Microsoft.Exchange.WebServices.Data.AutodiscoverLocalException: 
Autodiscover blocked a potentially insecure redirection to https://autodiscover-s.outlook.com/autodiscover/autodiscover.xml. 
To allow Autodiscover to follow the redirection, use the AutodiscoverUrl(string, AutodiscoverRedirectionUrlValidationCallback) overload.

            var service = new ExchangeService(ExchangeVersion.Exchange2007_SP1);
            service.UseDefaultCredentials = true;
            service.AutodiscoverUrl(emailSender);
            var email = new EmailMessage(service);
            email.ToRecipients.AddRange(emailToRecipients);
            email.CcRecipients.AddRange(emailCcRecipients);
            email.Subject = subject;
            email.Body = new MessageBody(body);
            email.Send();

service.AutodiscoverUrl(emailSender, delegate(string url) { return true; });

Ошибка : threw exception:
Microsoft.Exchange.WebServices.Data.AutodiscoverLocalException: 
Autodiscover blocked a potentially insecure redirection to https://autodiscover-s.outlook.com/autodiscover/autodiscover.xml. 
To allow Autodiscover to follow the redirection, use the AutodiscoverUrl(string, AutodiscoverRedirectionUrlValidationCallback) overload.

            var service = new ExchangeService(ExchangeVersion.Exchange2007_SP1);
            service.UseDefaultCredentials = true;
            service.AutodiscoverUrl(emailSender);
            var email = new EmailMessage(service);
            email.ToRecipients.AddRange(emailToRecipients);
            email.CcRecipients.AddRange(emailCcRecipients);
            email.Subject = subject;
            email.Body = new MessageBody(body);
            email.Send();

        private static async Task<string> GetTokenAsync()
        {
            var clientId = ConfigurationManager.AppSettings["ida:ClientId"];
            var clientSecret = ConfigurationManager.AppSettings["ida:ClientSecret"];
            var aadInstance = ConfigurationManager.AppSettings["ida:AADInstance"];

            var tenantId = ClaimsPrincipal.Current.FindFirst("http://schemas.microsoft.com/identity/claims/tenantid").Value;
            var userObjectId = ClaimsPrincipal.Current.FindFirst("http://schemas.microsoft.com/identity/claims/objectidentifier").Value;
            var signedInUserId = ClaimsPrincipal.Current.FindFirst(ClaimTypes.NameIdentifier).Value;

            var authoity = aadInstance + tenantId;
            var tokenCache = new ADALTokenCache(signedInUserId);
            const string resource = "https://graph.microsoft.com";
            var userIdentifier = new UserIdentifier(userObjectId, UserIdentifierType.UniqueId);

            var clientCredential = new ClientCredential(clientId, clientSecret);
            var authenticationContext = new AuthenticationContext(authoity, tokenCache);

            var authenticationResult = await authenticationContext.AcquireTokenSilentAsync(resource, clientCredential, userIdentifier);
            var token = authenticationResult.AccessToken;
            return token;
        }
  <appSettings>
    <add key="ida:ClientId" value="КлиентИдИзАжуры" />
    <add key="ida:TenantId" value="ТенатИдИзАжуры" />
    <add key="ida:ClientSecret" value="КлиентСекретИзАжуры" />
    <add key="ida:Domain" value="ВашаКомпания.onmicrosoft.com" />
    <add key="ida:AADInstance" value="https://login.microsoftonline.com/" />
    <add key="ida:PostLogoutRedirectUri" value="https://localhost:44365/" />
  </appSettings>