diff --git a/src/main/java/org/gcube/portal/socialnetworking/model/input/Message.java b/src/main/java/org/gcube/portal/socialnetworking/model/input/Message.java
index 63803e5..7e40d5a 100644
--- a/src/main/java/org/gcube/portal/socialnetworking/model/input/Message.java
+++ b/src/main/java/org/gcube/portal/socialnetworking/model/input/Message.java
@@ -5,6 +5,7 @@ import java.util.Calendar;
 import java.util.List;
 
 import javax.validation.constraints.NotNull;
+import javax.validation.constraints.Size;
 
 import com.fasterxml.jackson.annotation.JsonProperty;
 /**
@@ -18,10 +19,12 @@ public class Message {
 
 	@JsonProperty("subject")
 	@NotNull
+	@Size(min=1, message="subject cannot be empty")
 	private String subject;
 
 	@JsonProperty("body")
 	@NotNull
+	@Size(min=1, message="body cannot be empty")
 	private String body;
 
 	@JsonProperty("sender")
@@ -38,6 +41,7 @@ public class Message {
 
 	@JsonProperty("recipients")
 	@NotNull
+	@Size(min=1, message="recipient cannot be empty")
 	private List<Recipient> recipients;
 
 	public Message() {
@@ -130,7 +134,7 @@ public class Message {
 
 	@Override
 	public String toString() {
-		return "MessageOutputBeanMixIn [id=" + id + ", subject=" + subject
+		return "Message [id=" + id + ", subject=" + subject
 				+ ", body=" + body + ", senderId=" + senderId + ", sendTime="
 				+ sendTime + ", read=" + read + ", attachmentIds="
 				+ attachmentIds + ", recipients=" + recipients + "]";