Before we get to the EmailSender let’s talk about the who, what, when and where an admin email should consider. In the process of creating this article I discovered and corrected a couple of violations with my own admin emails.

Who

The who is usually a user name if a user is logged in or unknown if not. If you use a user name you risk violating the GDPR personal data rules. If you use the id of the user record and the record is deleted when the user requests to be forgotten it is no longer personal data. If you are using Identity in ASP.NET Core you can easily get the user record id with the UserManager.

var uid = _userManager.GetUserId(User);
if (uid == null)
{
    uid = "Unknown";
}

Or you can use System.Security.Claims.

var uid = "Unknown";
if (User.Identity.IsAuthenticated)
{
    uid = User.FindFirst(ClaimTypes.NameIdentifier).Value;
}

The browser’s User-Agent is not personal data.

string uaString = HttpContext.Request.Headers["User-Agent"].ToString();

The IP address is considered personal data. There are plenty of articles about IP anonymization for Google Analytics but not many for IP logging. Google Analytics anonymizes IP addresses by zeroing the last octant for IPv4 and last 5 hextets or doublets (80 bits) for IPv6. I have not seen many IPv6 addresses but we need to deal with it.

Section references:

We can get the IP address from HttpContext.Connection.RemoteIpAddress and I have created an extension to anonymize it.

What and When

Depends on the action the admin wants to be notified about. It could be as simple as a notice of a new registered user. The most important notice is when an error occurs. In a new ASP.NET Core web application the Startup.cs has app.UseExceptionHandler("/Error"); which redirects unhandled exceptions to an error page in the main Pages folder. You can get status codes from the error page if you add app.UseStatusCodePagesWithReExecute("/error/{0}"); to Startup.cs, the (int? statusCode = null) parameter to OnGet method in Error.cshtml.cs and "{statusCode?}" to the page directive in Error.cshtml. I thought I was sending an email with the exception details using var exception = HttpContext.Features.Get<IExceptionHandlerFeature>(); until I had a data foreign key issue which was throwing an exception and displaying the Error page but not sending the admin email. To capture exception details I had to send the admin email from exception handling middleware which will be subject of my next article.

Where

For a simple notice you can use Request.Path. To get the path where an error occurred you can use var feature = HttpContext.Features.Get<IStatusCodeReExecuteFeature>(); then feature?.OriginalPath in the OnGet of Error.cshtml.cs.

EmailSender

This article extends my previous article ASP.NET Core 2.2 - SMTP EmailSender Implementation. I use plain text for my admin email, but you can modify the method if you want html. The new method uses a new SysAdminEmail in EmailSettings.

Add the AnonymizeIpAddressExtention to the Services folder.

public static class AnonymizeIpAddressExtention
{
    //IPV4_NETMASK = "255.255.255.0";
    //IPV6_NETMASK = "ffff:ffff:ffff:0000:0000:0000:0000:0000";

    public static string AnonymizeIP(this IPAddress ipAddress)
    {
        string ipAnonymizedString;
        if (ipAddress != null)
        {
            if (ipAddress.AddressFamily == AddressFamily.InterNetwork)
            {
                var ipString = ipAddress.ToString();
                string[] octets = ipString.Split('.');
                octets[3] = "0";
                ipAnonymizedString = string.Join(".", octets);
            }
            else if (ipAddress.AddressFamily == AddressFamily.InterNetworkV6)
            {
                var ipString = ipAddress.ToString();
                string[] hextets = ipString.Split(':');
                var hl = hextets.Length;
                if ( hl > 3)
                {
                    for(var i = 3; i < hl; i++)
                    {
                        if(hextets[i].Length > 0)
                        {
                            hextets[i] = "0";
                        }
                    }
                }
                ipAnonymizedString = string.Join(":", hextets);
            }
            else
            {
                ipAnonymizedString = $"Not Valid - {ipAddress.ToString()}";
            }
        }
        else
        {
            ipAnonymizedString = "Is Null";
        }
        return ipAnonymizedString;
    }
}

Edit EmailSender.cs, add the signature to IEmailSender.

Task SendAdminEmailAsync(string subject, string textMessage, string uaString, string ipAnonymizedString, string userId);

Add the SendAdminEmailAsync method to EmailSender.

public async Task SendAdminEmailAsync(string subject, string textMessage, string uaString, string ipAnonymizedString, string userId)
{
    StringBuilder sb = new StringBuilder();

    sb.Append($"User Agent = {uaString} \r\n");

    sb.Append($"Anonymized IP = {ipAnonymizedString} \r\n");

    sb.Append($"User Id = {userId} \r\n \r\n");

    sb.Append(textMessage);

    try
    {
        var mimeMessage = new MimeMessage();
        mimeMessage.From.Add(new MailboxAddress(_emailSettings.Sender));
        mimeMessage.To.Add(new MailboxAddress(_emailSettings.SysAdminEmail));

        mimeMessage.Subject = subject;

        mimeMessage.Body = new TextPart("plain")
        {
            Text = sb.ToString()
        };

        using (var client = new SmtpClient())
        {
            // For demo-purposes, accept all SSL certificates (in case the server supports STARTTLS)
            client.ServerCertificateValidationCallback = (s, c, h, e) => true;

            if (_env.IsDevelopment())
            {
                await client.ConnectAsync(_emailSettings.MailServer, _emailSettings.MailPort, true);
            }
            else
            {
                await client.ConnectAsync(_emailSettings.MailServer);
            }

            // Note: only needed if the SMTP server requires authentication
            await client.AuthenticateAsync(_emailSettings.Sender, _emailSettings.Password);

            await client.SendAsync(mimeMessage);

            await client.DisconnectAsync(true);
        }
    }
    catch (Exception ex)
    {
        // TODO: handle exception
        throw new InvalidOperationException(ex.Message);
    }
}