Detect Disposable Email Addresses

Published 1st May 2020 by Jonathan Purdom

A common problem with signing up users for a newsletter or a trial is to try and prevent a user registering with a disposable email address. The best list that I can find of disposable email addresses is here :

Ivolo/is-disposable-email (Github)

I have created a script that uses the HttpClient to download a list of disposable addresses from GitHub. The list can then be stored in a database table and used to validate a users email domain when registering for a newsletter or account.

Disposable Email Service

There are two classes defined :

DisposableEmailResponse - This contains the service response (success, error message, list of domains)
DisposableEmailService - This gets the list of Disposable Email Domains

using System.Net.Http
using System.Net.Mail
using System.Threading.Tasks
using Newtonsoft.Json


public class DisposableEmailResponse
{
    public bool IsSuccess { get; set; }
    public string ErrorMessage { get; set; }
    public IEnumerable<string> DisposableEmailDomains { get; set; } = new List<string>();
}

public class DisposableEmailService
{
    public async Task<DisposableEmailResponse> Get(CancellationToken cancellationToken)
    {
        const string GithubBlacklist
        = "https://raw.githubusercontent.com/ivolo/disposable-email-domains/master/index.json";

        var result = new DisposableEmailResponse();


        using (var client = new HttpClient())
        {
            try
            {
                var response = await client.GetAsync(GithubBlacklist, cancellationToken);

                response.EnsureSuccessStatusCode();

                var contents = await response.Content.ReadAsStringAsync();
                result.IsSuccess = true;
                result.DisposableEmailDomains = JsonConvert.DeserializeObject<List<string>>(contents);

            }
            catch (TaskCanceledException)
            {
                result.ErrorMessage = $"{nameof(Get)} task has been cancelled";

            }
            catch (Exception ex)
            {
                result.ErrorMessage = $"{nameof(Get)} has errored : {ex.Message}";
            }

        }
        return result;

    }
}

Usage

I use LINQPad as my default scratchpad for creating scripts and services. The script above references the following nuget packages

Newtonsoft.Json

The code below shows how to use the DisposableEmailService

async Task Main()
{
    var disposableEmails = await GetDisposableEmailAddresses();

    var testEmail = "chethostat@matra.site";
    var mailAddress = new MailAddress(testEmail);
    var domainPart = mailAddress.Host.ToLower();

    if (disposableEmails.Contains(domainPart))
        Console.Write($"The email is invalid {testEmail}, Disposable email addresses are disallowed from registering");

}

public async Task<List<string>> GetDisposableEmailAddresses()
{
    var token = new CancellationToken();
    var disposableEmailService = new DisposableEmailService();
    var disposableEmails = await disposableEmailService.Get(token);
    return disposableEmails.DisposableEmailDomains.ToList();
}