在ASP.NET Core中，如果身份验证未发送电子邮件，则可以使用以下代码示例来解决该问题：

1. 首先，确保您的应用程序已正确配置电子邮件设置。在appsettings.json文件中添加以下内容：

"EmailSettings": {
  "SmtpServer": "your_smtp_server",
  "Port": 587,
  "UserName": "your_username",
  "Password": "your_password"
}

2. 创建一个名为EmailSender的接口，定义一个发送电子邮件的方法：

public interface IEmailSender
{
    Task SendEmailAsync(string email, string subject, string message);
}

3. 实现EmailSender接口的具体类：

public class EmailSender : IEmailSender
{
    private readonly EmailSettings _emailSettings;

    public EmailSender(IOptions emailSettings)
    {
        _emailSettings = emailSettings.Value;
    }

    public Task SendEmailAsync(string email, string subject, string message)
    {
        var client = new SmtpClient(_emailSettings.SmtpServer, _emailSettings.Port)
        {
            UseDefaultCredentials = false,
            Credentials = new NetworkCredential(_emailSettings.UserName, _emailSettings.Password),
            EnableSsl = true
        };

        var mailMessage = new MailMessage
        {
            From = new MailAddress(_emailSettings.UserName),
            Subject = subject,
            Body = message,
            IsBodyHtml = true
        };
        mailMessage.To.Add(email);

        return client.SendMailAsync(mailMessage);
    }
}

4. 在Startup.cs文件中进行配置和注册服务：

public void ConfigureServices(IServiceCollection services)
{
    // ...

    services.Configure(Configuration.GetSection("EmailSettings"));
    services.AddTransient();

    // ...
}

5. 在需要发送电子邮件的地方注入IEmailSender并使用它来发送邮件：

private readonly IEmailSender _emailSender;

public YourController(IEmailSender emailSender)
{
    _emailSender = emailSender;
}

public async Task SendEmail()
{
    // ...

    await _emailSender.SendEmailAsync(email, subject, message);

    // ...
}

通过以上步骤，您就可以在ASP.NET Core中发送电子邮件进行身份验证了。请确保您的电子邮件设置正确，并替换实际的SMTP服务器、用户名和密码。