diff --git a/src/Postmark/PostmarkAdminClient.cs b/src/Postmark/PostmarkAdminClient.cs
index c97b95c..6ea769b 100644
--- a/src/Postmark/PostmarkAdminClient.cs
+++ b/src/Postmark/PostmarkAdminClient.cs
@@ -19,8 +19,9 @@ public class PostmarkAdminClient : PostmarkDotNet.PostmarkClientBase
         /// </summary>
         /// <param name="accountToken">The "accountToken" can be found by logging into your Postmark and navigating to https://postmarkapp.com/account/edit - Keep this token secret and safe.</param>
         /// <param name="apiBaseUri">Optionally override the base url to the API. For example, you may fallback to HTTP (non-SSL) if your app requires it, though, this is not recommended.</param>
-        public PostmarkAdminClient(string accountToken, string apiBaseUri = "https://api.postmarkapp.com")
-            : base(apiBaseUri)
+        /// <param name="client"><see cref="ISimpleHttpClient"/> to processes HTTP interactions.</param>
+        public PostmarkAdminClient(string accountToken, string apiBaseUri = "https://api.postmarkapp.com", ISimpleHttpClient client = null)
+            : base(apiBaseUri, client)
         {
             _authToken = accountToken;
         }
@@ -112,7 +113,7 @@ public async Task<PostmarkServer> CreateServerAsync(String name, string color =
         public async Task<PostmarkServer> EditServerAsync(int serverId, String name = null, string color = null,
             bool? rawEmailEnabled = null, bool? smtpApiActivated = null, string inboundHookUrl = null,
             string bounceHookUrl = null, string openHookUrl = null, bool? postFirstOpenOnly = null,
-            bool? trackOpens = null, string inboundDomain = null, int? inboundSpamThreshold = null, 
+            bool? trackOpens = null, string inboundDomain = null, int? inboundSpamThreshold = null,
             LinkTrackingOptions? trackLinks = null, string clickHookUrl = null, string deliveryHookUrl = null, bool? enableSmtpApiErrorHooks = null)
         {
 
diff --git a/src/Postmark/PostmarkClient.cs b/src/Postmark/PostmarkClient.cs
index 820b42d..0ce2f70 100644
--- a/src/Postmark/PostmarkClient.cs
+++ b/src/Postmark/PostmarkClient.cs
@@ -33,8 +33,9 @@ protected override string AuthHeaderName
         /// </summary>
         /// <param name="apiBaseUri">The base uri to use when connecting to Postmark. You should rarely need to modify this, except if you want to disable TLS (not recommended), or you are using a proxy of some sort to connect to the API.</param>
         /// <param name="serverToken">Used for requests that require server level privileges. This token can be found on the Credentials tab under your Postmark server.</param>
-        public PostmarkClient(string serverToken, string apiBaseUri = "https://api.postmarkapp.com")
-            : base(apiBaseUri)
+        /// <param name="client"><see cref="ISimpleHttpClient"/> to processes HTTP interactions.</param>
+        public PostmarkClient(string serverToken, string apiBaseUri = "https://api.postmarkapp.com", ISimpleHttpClient client = null)
+            : base(apiBaseUri, client)
         {
             _authToken = serverToken;
         }
diff --git a/src/Postmark/PostmarkClientBase.cs b/src/Postmark/PostmarkClientBase.cs
index b5c4761..cc93c2e 100644
--- a/src/Postmark/PostmarkClientBase.cs
+++ b/src/Postmark/PostmarkClientBase.cs
@@ -14,19 +14,6 @@ namespace PostmarkDotNet
     /// </summary>
     public abstract class PostmarkClientBase
     {
-        private static Lazy<ISimpleHttpClient> _staticClient = 
-            new Lazy<ISimpleHttpClient>(()=>new SimpleHttpClient()) ;
-
-        /// <summary>
-        /// Configure a global connection factory to to process HTTP interactions.
-        /// </summary>
-        /// <remarks>
-        /// In most cases, you should not need to modify this property, but it's useful
-        /// in cases where you want to use another http client, or to mock the http processing
-        /// (for tests).
-        /// </remarks>
-        public static Func<ISimpleHttpClient> ClientFactory {get;set;} = () => _staticClient.Value;
-
         protected static readonly string DATE_FORMAT = "yyyy-MM-dd";
 
         /// <summary>
@@ -38,15 +25,17 @@ public abstract class PostmarkClientBase
               typeof(PostmarkClient).AssemblyQualifiedName + ")";
 
         private Uri baseUri;
+        private readonly ISimpleHttpClient client;
 
         /// <summary>
         /// Provides a base implementation of core request/response interactions.
         /// </summary>
         /// <param name="apiBaseUri"></param>
-        /// <param name="requestTimeoutInSeconds"></param>
-        public PostmarkClientBase(string apiBaseUri = "https://api.postmarkapp.com")
+        /// <param name="client"><see cref="ISimpleHttpClient"/> to processes HTTP interactions.</param>
+        public PostmarkClientBase(string apiBaseUri = "https://api.postmarkapp.com", ISimpleHttpClient client = null)
         {
             baseUri = new Uri(apiBaseUri);
+            this.client = client ?? new SimpleHttpClient();
         }
 
         protected abstract string AuthHeaderName { get; }
@@ -68,8 +57,6 @@ protected async Task<TResponse> ProcessRequestAsync<TRequestBody, TResponse>(str
         {
             TResponse retval = default(TResponse);
 
-            var client = ClientFactory();
-            
             var request = new HttpRequestMessage(verb, baseUri + apiPath.TrimStart('/'));
 
             //if the message is not a string, or the message is a non-empty string,