Alternative approach. Use IHttpClientFactory for MailGunSender

src/Senders/FluentEmail.Mailgun/FluentEmail.Mailgun.csproj

@@ -8,6 +8,7 @@
   </PropertyGroup>
 
   <ItemGroup>
+    <PackageReference Include="Microsoft.Extensions.Http" Version="6.0.0" />
     <PackageReference Include="Newtonsoft.Json" Version="12.0.3" />
   </ItemGroup>
 

src/Senders/FluentEmail.Mailgun/FluentEmailMailgunBuilderExtensions.cs

@@ -1,4 +1,8 @@
-using FluentEmail.Core.Interfaces;
+using System;
+using System.Net.Http.Headers;
+using System.Net.Http;
+using System.Text;
+using FluentEmail.Core.Interfaces;
 using FluentEmail.Mailgun;
 using Microsoft.Extensions.DependencyInjection.Extensions;
 
@@ -8,7 +12,28 @@ public static class FluentEmailMailgunBuilderExtensions
     {
         public static FluentEmailServicesBuilder AddMailGunSender(this FluentEmailServicesBuilder builder, string domainName, string apiKey, MailGunRegion mailGunRegion = MailGunRegion.USA)
         {
-            builder.Services.TryAdd(ServiceDescriptor.Scoped<ISender>(_ => new MailgunSender(domainName, apiKey, mailGunRegion)));
+            builder.Services.AddHttpClient(nameof(MailgunSender),
+                client =>
+                {
+                    string url = string.Empty;
+                    switch (mailGunRegion)
+                    {                        
+                        case MailGunRegion.USA:
+                            url = $"https://api.mailgun.net/v3/{domainName}/";
+                            break;
+                        case MailGunRegion.EU:
+                            url = $"https://api.eu.mailgun.net/v3/{domainName}/";
+                            break;
+
+                        default:
+                            throw new ArgumentException($"'{mailGunRegion}' is not a valid value for {nameof(mailGunRegion)}");
+                    }
+
+                    client.BaseAddress = new Uri(url);
+                    client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Basic", Convert.ToBase64String(Encoding.ASCII.GetBytes($"api:{apiKey}")));
+                });
+
+            builder.Services.TryAdd(ServiceDescriptor.Scoped<ISender, MailgunSender>());
             return builder;
         }
     }

src/Senders/FluentEmail.Mailgun/MailgunSender.cs

@@ -1,9 +1,6 @@
-using System;
-using System.Collections.Generic;
+using System.Collections.Generic;
 using System.Linq;
 using System.Net.Http;
-using System.Net.Http.Headers;
-using System.Text;
 using System.Threading;
 using System.Threading.Tasks;
 using FluentEmail.Core;
@@ -15,33 +12,11 @@ namespace FluentEmail.Mailgun
 {
     public class MailgunSender : ISender
     {
-        private readonly string _apiKey;
-        private readonly string _domainName;
-        private HttpClient _httpClient;
+        private readonly HttpClient _httpClient;
 
-        public MailgunSender(string domainName, string apiKey, MailGunRegion mailGunRegion = MailGunRegion.USA)
-        {
-            _domainName = domainName;
-            _apiKey = apiKey;
-            string url = string.Empty;
-            switch(mailGunRegion)
-            {
-                case MailGunRegion.USA:
-                    url = $"https://api.mailgun.net/v3/{_domainName}/";
-                    break;
-                case MailGunRegion.EU:
-                    url = $"https://api.eu.mailgun.net/v3/{_domainName}/";
-                    break;
-
-                default:
-                    throw new ArgumentException($"'{mailGunRegion}' is not a valid value for {nameof(mailGunRegion)}");
-            }
-            _httpClient = new HttpClient
-            {
-                BaseAddress = new Uri(url)
-            };
-
-            _httpClient.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Basic", Convert.ToBase64String(Encoding.ASCII.GetBytes($"api:{_apiKey}")));
+        public MailgunSender(IHttpClientFactory httpClientfactory)
+        {              
+            _httpClient = httpClientfactory.CreateClient(nameof(MailgunSender));           
         }
 
         public SendResponse Send(IFluentEmail email, CancellationToken? token = null)

test/FluentEmail.Core.Tests/FluentEmail.Core.Tests.csproj

@@ -14,6 +14,7 @@
 
   <ItemGroup>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.8.3" />
+    <PackageReference Include="Moq" Version="4.20.70" />
     <PackageReference Include="NUnit" Version="3.13.0" />
     <PackageReference Include="NUnit3TestAdapter" Version="3.17.0" />
     <ProjectReference Include="..\..\src\Senders\FluentEmail.Mailtrap\FluentEmail.Mailtrap.csproj" />

test/FluentEmail.Core.Tests/MailgunSenderTests.cs

@@ -4,6 +4,8 @@
 using FluentEmail.Core.Models;
 using NUnit.Framework;
 using Newtonsoft.Json;
+using System.Net.Http;
+using Moq;
 
 namespace FluentEmail.Mailgun.Tests
 {
@@ -17,7 +19,7 @@ public class MailgunSenderTests
         [SetUp]
         public void SetUp()
         {
-            var sender = new MailgunSender("sandboxcf5f41bbf2f84f15a386c60e253b5fe9.mailgun.org", "key-8d32c046d7f14ada8d5ba8253e3e30de");
+            var sender = new MailgunSender(Mock.Of<IHttpClientFactory>());
             Email.DefaultSender = sender;
         }