Try using a TransportListener to listen for delivery errors.

This is somewhat temporary code to try something out...
In our production environment there are mails getting lost.
I'd like to find out why.
Try using a TransportListener. This is more complicated.
Also the listener may be getting added many times. We shall see.

src/main/java/com/samskivert/net/MailUtil.java

@@ -8,9 +8,13 @@ package com.samskivert.net;
 import java.io.IOException;
 import java.util.Properties;
 
+import javax.mail.Address;
 import javax.mail.Message;
+import javax.mail.NoSuchProviderException;
 import javax.mail.Session;
 import javax.mail.Transport;
+import javax.mail.event.TransportEvent;
+import javax.mail.event.TransportListener;
 import javax.mail.internet.InternetAddress;
 import javax.mail.internet.MimeMessage;
 
@@ -18,6 +22,8 @@ import java.util.regex.Pattern;
 
 import com.samskivert.util.StringUtil;
 
+import static com.samskivert.net.Log.log;
+
 /**
  * The mail util class encapsulates some utility functions related to
  * sending emails.
@@ -119,6 +125,7 @@ public class MailUtil
                                     String subject, MimeMessage message)
         throws IOException
     {
+        checkCreateSession();
         try {
             message.setFrom(new InternetAddress(sender));
             for (String recipient : recipients) {
@@ -127,7 +134,15 @@ public class MailUtil
             if (subject != null) {
                 message.setSubject(subject);
             }
-            Transport.send(message);
+            message.saveChanges();
+            Address[] recips = message.getAllRecipients();
+            if (recips.length == 0) {
+                return;
+            }
+            Transport t = _defaultSession.getTransport(recips[0]);
+            t.addTransportListener(_listener);
+            t.connect();
+            t.sendMessage(message, recips);
 
         } catch (Exception e) {
             String errmsg = "Failure sending mail [from=" + sender +
@@ -144,13 +159,36 @@ public class MailUtil
      */
     public static final MimeMessage createEmptyMessage ()
     {
-        Properties props = System.getProperties();
-        if (props.getProperty("mail.smtp.host") == null) {
-            props.put("mail.smtp.host", "localhost");
-        }
-        return new MimeMessage(Session.getDefaultInstance(props, null));
+        checkCreateSession();
+        return new MimeMessage(_defaultSession);
     }
 
+    protected static void checkCreateSession ()
+    {
+        if (_defaultSession == null) {
+            Properties props = System.getProperties();
+            if (props.getProperty("mail.smtp.host") == null) {
+                props.put("mail.smtp.host", "localhost");
+            }
+            _defaultSession = Session.getDefaultInstance(props, null);
+        }
+    }
+
+    protected static Session _defaultSession;
+
+    protected static TransportListener _listener = new TransportListener()
+        {
+            public void messageDelivered (TransportEvent event) {
+                log.info("messageDelivered: " + event);
+            }
+            public void messageNotDelivered (TransportEvent event) {
+                log.info("messageNotDelivered: " + event);
+            }
+            public void messagePartiallyDelivered (TransportEvent event) {
+                log.info("messagePartiallyDelivered: " + event);
+            }
+        };
+
     /** Originally formulated by lambert@nas.nasa.gov. */
     protected static final String EMAIL_REGEX = "^([-A-Za-z0-9_.!%+]+@" +
         "[-a-zA-Z0-9]+(\\.[-a-zA-Z0-9]+)*\\.[-a-zA-Z0-9]+)$";