diff --git a/src/main/java/org/simplejavamail/mailer/internal/mailsender/MailSender.java b/src/main/java/org/simplejavamail/mailer/internal/mailsender/MailSender.java
index af668e508..a0069b984 100644
--- a/src/main/java/org/simplejavamail/mailer/internal/mailsender/MailSender.java
+++ b/src/main/java/org/simplejavamail/mailer/internal/mailsender/MailSender.java
@@ -25,8 +25,6 @@
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 import java.util.concurrent.Phaser;
-import java.util.concurrent.ThreadFactory;
-import java.util.concurrent.atomic.AtomicInteger;
 
 import static java.lang.String.format;
 import static org.simplejavamail.converter.EmailConverter.mimeMessageToEML;
@@ -72,7 +70,7 @@ public class MailSender {
 	 * Only set when {@link ProxyConfig} is provided with authentication details.
 	 */
 	@Nullable
-	private AnonymousSocks5Server proxyServer = null;
+	private AnonymousSocks5Server proxyServer;
 
 	/**
 	 * Allows us to manage how many thread we run at the same time using a thread pool.
@@ -194,21 +192,9 @@ the proxy bridge server (or connection pool in async mode) while a non-async ema
         smtpRequestsPhaser.register();
 		if (async) {
 			// start up thread pool if necessary
-			if (executor == null) {
-				executor = Executors.newFixedThreadPool(operationalConfig.getThreadPoolSize(), new ThreadFactory() {
-					final AtomicInteger threadCounter = new AtomicInteger(0);
-					@Override
-					public Thread newThread(Runnable r) {
-						Thread thread = new Thread(r, "Simple Java Mail async mail sender #" + threadCounter.getAndIncrement());
-						if (!thread.isDaemon()) {
-							thread.setDaemon(true);
-						}
-						if (thread.getPriority() != Thread.NORM_PRIORITY) {
-							thread.setPriority(Thread.NORM_PRIORITY);
-						}
-						return thread;
-					}
-				});
+			if (executor == null || executor.isShutdown()) {
+				executor = Executors.newFixedThreadPool(operationalConfig.getThreadPoolSize(),
+						new NamedThreadFactory("Simple Java Mail async mail sender"));
 			}
 			configureSessionWithTimeout(session, operationalConfig.getSessionTimeout());
 			executor.execute(new Runnable() {
@@ -269,7 +255,6 @@ private void sendMailClosure(@Nonnull final Session session, @Nonnull final Emai
 
 			try {
 				synchronized (this) {
-					//noinspection ConstantConditions
 					if (needsAuthenticatedProxy() && !proxyServer.isRunning()) {
 						LOGGER.trace("starting proxy bridge");
 						proxyServer.start();
@@ -319,7 +304,7 @@ private void configureBounceToAddress(final Session session, final Email email)
 	}
 	
 	/**
-	 * We need to keep a count of running threads in case a proxyserver is running
+	 * We need to keep a count of running threads in case a proxyserver is running or a connection pool needs to be shut down.
      */
     private synchronized void checkShutDownRunningProcesses() {
         smtpRequestsPhaser.arriveAndDeregister();
@@ -327,11 +312,15 @@ private synchronized void checkShutDownRunningProcesses() {
         // if this thread is the last one finishing
         if (smtpRequestsPhaser.getUnarrivedParties() == 0) {
             LOGGER.trace("all threads have finished processing");
-			//noinspection ConstantConditions
 			if (needsAuthenticatedProxy() && proxyServer.isRunning() && !proxyServer.isStopping()) {
                 LOGGER.trace("stopping proxy bridge...");
                 proxyServer.stop();
             }
+            // shutdown the threadpool, or else the Mailer will keep any JVM alive forever
+            // executor is only available in async mode
+            if (executor != null) {
+                executor.shutdown();
+            }
         }
     }
 
@@ -389,7 +378,6 @@ public synchronized void testConnection() {
 		logSession(session, "connection test");
 
 		try (Transport transport = session.getTransport()) {
-			//noinspection ConstantConditions
 			if (needsAuthenticatedProxy() && !proxyServer.isRunning()) {
 				LOGGER.trace("starting proxy bridge for testing connection");
 				proxyServer.start();
diff --git a/src/main/java/org/simplejavamail/mailer/internal/mailsender/NamedThreadFactory.java b/src/main/java/org/simplejavamail/mailer/internal/mailsender/NamedThreadFactory.java
new file mode 100644
index 000000000..70940ebf1
--- /dev/null
+++ b/src/main/java/org/simplejavamail/mailer/internal/mailsender/NamedThreadFactory.java
@@ -0,0 +1,30 @@
+package org.simplejavamail.mailer.internal.mailsender;
+
+import javax.annotation.Nonnull;
+import java.util.concurrent.ThreadFactory;
+import java.util.concurrent.atomic.AtomicInteger;
+
+import static java.lang.String.format;
+import static java.lang.Thread.currentThread;
+
+class NamedThreadFactory implements ThreadFactory {
+	private final AtomicInteger threadNumber = new AtomicInteger(1);
+	private final ThreadGroup group;
+	private final String threadName;
+	
+	NamedThreadFactory(@Nonnull final String threadName) {
+		SecurityManager s = System.getSecurityManager();
+		group = (s != null) ? s.getThreadGroup() : currentThread().getThreadGroup();
+		this.threadName = threadName;
+	}
+	
+	@Nonnull
+	public Thread newThread(@Nonnull Runnable r) {
+		Thread t = new Thread(group, r, format("%s %d", threadName, threadNumber.getAndIncrement()));
+		if (t.isDaemon())
+			t.setDaemon(false);
+		if (t.getPriority() != Thread.NORM_PRIORITY)
+			t.setPriority(Thread.NORM_PRIORITY);
+		return t;
+	}
+}