diff --git a/logback-classic-blackbox/src/test/java/ch/qos/logback/classic/blackbox/net/SMTPAppender_GreenTest.java b/logback-classic-blackbox/src/test/java/ch/qos/logback/classic/blackbox/net/SMTPAppender_GreenTest.java
index d514f0dc9a..162422ad95 100644
--- a/logback-classic-blackbox/src/test/java/ch/qos/logback/classic/blackbox/net/SMTPAppender_GreenTest.java
+++ b/logback-classic-blackbox/src/test/java/ch/qos/logback/classic/blackbox/net/SMTPAppender_GreenTest.java
@@ -151,6 +151,9 @@ private MimeMultipart verifyAndExtractMimeMultipart(String subject)
         int expectedEmailCount = 1;
         // wait for the server to receive the messages
         waitForServerToReceiveEmails(expectedEmailCount);
+        while (!ch.qos.logback.core.net.SMTPAppenderBase.getExecutionStatus()) {
+            Thread.yield();
+        }
         MimeMessage[] mma = greenMailServer.getReceivedMessages();
         assertNotNull(mma);
         assertEquals(expectedEmailCount, mma.length);
@@ -304,6 +307,7 @@ private void configure(String file) throws JoranException {
 
     @Test
     public void testCustomEvaluator() throws Exception {
+        ch.qos.logback.core.net.SMTPAppenderBase.reset();
         startSMTPServer(NO_SSL);
         configure(BlackboxClassicTestConstants.JORAN_INPUT_PREFIX + "smtp/customEvaluator.xml");
 
diff --git a/logback-core/src/main/java/ch/qos/logback/core/net/SMTPAppenderBase.java b/logback-core/src/main/java/ch/qos/logback/core/net/SMTPAppenderBase.java
index eb0cd1e4fb..8c74a2b9f3 100755
--- a/logback-core/src/main/java/ch/qos/logback/core/net/SMTPAppenderBase.java
+++ b/logback-core/src/main/java/ch/qos/logback/core/net/SMTPAppenderBase.java
@@ -70,6 +70,7 @@ public abstract class SMTPAppenderBase<E> extends AppenderBase<E> {
     protected Layout<E> subjectLayout;
     protected Layout<E> layout;
 
+    public static volatile boolean hasExecuted;
     private List<PatternLayoutBase<E>> toPatternLayoutList = new ArrayList<PatternLayoutBase<E>>();
     private String from;
     private String subjectStr = null;
@@ -650,6 +651,14 @@ public void setSessionViaJNDI(boolean sessionViaJNDI) {
         this.sessionViaJNDI = sessionViaJNDI;
     }
 
+    public static boolean getExecutionStatus() {
+        return hasExecuted;
+    }
+
+    public static void reset() {
+        hasExecuted = false;
+    }
+
     /**
      * Set the character set encoding of the outgoing email messages. The default
      * encoding is "UTF-8" which usually works well for most purposes.
@@ -680,6 +689,7 @@ class SenderRunnable implements Runnable {
 
         public void run() {
             sendBuffer(cyclicBuffer, e);
+            hasExecuted = true;
         }
     }
 }