diff --git a/src/main/java/module/mailtracking/presentationTier/MailTrackingAction.java b/src/main/java/module/mailtracking/presentationTier/MailTrackingAction.java
index a6c099d..c5a42e2 100644
--- a/src/main/java/module/mailtracking/presentationTier/MailTrackingAction.java
+++ b/src/main/java/module/mailtracking/presentationTier/MailTrackingAction.java
@@ -44,6 +44,8 @@
 import module.mailtracking.domain.exception.PermissionDeniedException;
 
 import org.apache.commons.beanutils.BeanComparator;
+import org.apache.commons.collections.CollectionUtils;
+import org.apache.commons.collections.Predicate;
 import org.apache.commons.lang.StringUtils;
 import org.apache.struts.action.ActionForm;
 import org.apache.struts.action.ActionForward;
@@ -258,7 +260,7 @@ public ActionForward addNewEntry(final ActionMapping mapping, final ActionForm f
             throw new PermissionDeniedException();
         }
 
-        if (!preValidate(readCorrespondenceEntryBean(request), request)) {
+        if (!preValidate(readCorrespondenceEntryBean(request), request, readCorrespondenceTypeView(request))) {
             RenderUtils.invalidateViewState("associate.document.bean");
             setAssociateDocumentBean(request, null);
             return prepareCreateNewEntry(mapping, form, request, response);
@@ -301,7 +303,8 @@ public ActionForward addNewEntryInvalid(final ActionMapping mapping, final Actio
     private static final Integer MAX_SENDER_SIZE = 50;
     private static final Integer MAX_RECIPIENT_SIZE = 50;
 
-    protected boolean preValidate(CorrespondenceEntryBean correspondenceEntryBean, HttpServletRequest request) {
+    protected boolean preValidate(CorrespondenceEntryBean correspondenceEntryBean, HttpServletRequest request,
+            CorrespondenceType correspondenceType) {
         if (StringUtils.isEmpty(correspondenceEntryBean.getSender())) {
             addMessage(request, "error.mail.tracking.sender.is.required");
             return false;
@@ -323,6 +326,22 @@ protected boolean preValidate(CorrespondenceEntryBean correspondenceEntryBean, H
             return false;
         }
 
+        final String reference = correspondenceEntryBean.getReference();
+        final CorrespondenceEntry entry = correspondenceEntryBean.getEntry();
+
+        if (CollectionUtils.select(correspondenceEntryBean.getMailTracking().getActiveEntries(correspondenceType),
+                new Predicate() {
+
+                    @Override
+                    public boolean evaluate(Object arg0) {
+                        return ((CorrespondenceEntry) arg0).getReference().equals(reference)
+                                && ((CorrespondenceEntry) arg0) != entry; // if they are the same
+                    }
+                }).size() >= 1) {
+            addMessage(request, "error.mail.tracking.reference.duplicated");
+            return false;
+        }
+
         return true;
     }
 
@@ -343,7 +362,7 @@ public final ActionForward editEntry(final ActionMapping mapping, final ActionFo
             final HttpServletResponse response) throws Exception {
         MailTracking mailTracking = readMailTracking(request);
 
-        if (!preValidate(readCorrespondenceEntryBean(request), request)) {
+        if (!preValidate(readCorrespondenceEntryBean(request), request, readCorrespondenceTypeView(request))) {
             return prepareEditEntry(mapping, form, request, response);
         }
 
diff --git a/src/main/java/module/mailtracking/presentationTier/ajax/MailTrackingAction.java b/src/main/java/module/mailtracking/presentationTier/ajax/MailTrackingAction.java
index 6474425..f0a5e11 100644
--- a/src/main/java/module/mailtracking/presentationTier/ajax/MailTrackingAction.java
+++ b/src/main/java/module/mailtracking/presentationTier/ajax/MailTrackingAction.java
@@ -75,7 +75,7 @@ public final ActionForward addNewEntry(final ActionMapping mapping, final Action
             throw new PermissionDeniedException();
         }
 
-        if (!preValidate(readCorrespondenceEntryBean(request), request)) {
+        if (!preValidate(readCorrespondenceEntryBean(request), request, readCorrespondenceTypeView(request))) {
             RenderUtils.invalidateViewState("associate.document.bean");
             setAssociateDocumentBean(request, null);
             return prepareCreateNewEntry(mapping, form, request, response);
diff --git a/src/main/resources/resources/MailTrackingResources.properties b/src/main/resources/resources/MailTrackingResources.properties
index 9dfb51c..9a73d1b 100644
--- a/src/main/resources/resources/MailTrackingResources.properties
+++ b/src/main/resources/resources/MailTrackingResources.properties
@@ -128,6 +128,7 @@ label.reason=Motivo
 messsage.mail.tracking.deletion.reason.necessary=Indique o motivo remoção deste registo
 
 error.mail.tracking.sender.is.required=O remetente é obrigatório
+error.mail.tracking.reference.duplicated=A referência já existe
 error.mail.tracking.sender.length.must.be.less.than=O tamanho máximo para o campo remetente é de {0}
 error.mail.tracking.recipient.is.required=O destinatário é obrigatório
 error.mail.tracking.recipient.length.must.be.less.than=O tamanho máximo para o campo de destinatário é de {0}
diff --git a/src/main/webapp/mailtracking/editCorrespondenceEntry.jsp b/src/main/webapp/mailtracking/editCorrespondenceEntry.jsp
index 8dcb4d4..33637b6 100644
--- a/src/main/webapp/mailtracking/editCorrespondenceEntry.jsp
+++ b/src/main/webapp/mailtracking/editCorrespondenceEntry.jsp
@@ -28,7 +28,7 @@
 </div>
 
 
-<fr:form id="add.new.entry.form" action="<%= "/mailtracking.do?method=editEntry&amp;mailTrackingId=" + mailTrackingId + "&amp;correspondenceType=" + correspondenceType %>">
+<fr:form id="add.new.entry.form" action="<%= "/mailtracking.do?method=editEntry&amp;mailTrackingId=" + mailTrackingId + "&amp;entryId="+ entryId + "&amp;correspondenceType=" + correspondenceType %>">
 	<fr:edit id="correspondence.entry.bean" name="correspondenceEntryBean" visible="false" />
 	
 	<fr:edit id="correspondence.entry.bean.data" name="correspondenceEntryBean" schema="<%= CorrespondenceType.RECEIVED.name().equals(correspondenceType) ? "module.mailtracking.correspondence.received.entry.edit" : "module.mailtracking.correspondence.sent.entry.edit" %>" >