Let MailboxMessage extend ExpirablePayload:

For all MailboxMessage we want to be sure they have an expire date.
Add getTTL methods and TTL value.
We use 7 days for ChatMessages and 30 days for PrivateNotificationMessages.
All others use default 15 days.
We prefer to keep them explicit and not use a default method in
ExpirablePayload or MailboxMessage.
The value in PrefixedSealedAndSignedMessage will not be used as the
sender use the TTL of the payload and pass that to the MailboxStoragePayload
where we store it in the extraMap. That way we can use different TTL even the
payload message is encrypted and we would not be able to look it up.

core/src/main/java/bisq/core/alert/PrivateNotificationMessage.java

@@ -23,12 +23,16 @@ import bisq.network.p2p.mailbox.MailboxMessage;
 import bisq.common.app.Version;
 import bisq.common.proto.network.NetworkEnvelope;
 
+import java.util.concurrent.TimeUnit;
+
 import lombok.EqualsAndHashCode;
 import lombok.Value;
 
 @EqualsAndHashCode(callSuper = true)
 @Value
 public class PrivateNotificationMessage extends NetworkEnvelope implements MailboxMessage {
+    public static final long TTL = TimeUnit.DAYS.toMillis(30);
+
     private final PrivateNotificationPayload privateNotificationPayload;
     private final NodeAddress senderNodeAddress;
     private final String uid;
@@ -70,4 +74,9 @@ public class PrivateNotificationMessage extends NetworkEnvelope implements Mailb
                 proto.getUid(),
                 messageVersion);
     }
+
+    @Override
+    public long getTTL() {
+        return TTL;
+    }
 }

core/src/main/java/bisq/core/support/dispute/messages/DisputeMessage.java

@@ -20,9 +20,18 @@ package bisq.core.support.dispute.messages;
 import bisq.core.support.SupportType;
 import bisq.core.support.messages.SupportMessage;
 
+import java.util.concurrent.TimeUnit;
+
 public abstract class DisputeMessage extends SupportMessage {
+    public static final long TTL = TimeUnit.DAYS.toMillis(15);
 
     public DisputeMessage(int messageVersion, String uid, SupportType supportType) {
         super(messageVersion, uid, supportType);
     }
+
+    @Override
+    public long getTTL() {
+        return TTL;
+    }
+
 }

core/src/main/java/bisq/core/support/messages/ChatMessage.java

@@ -39,6 +39,7 @@ import java.util.Date;
 import java.util.List;
 import java.util.Optional;
 import java.util.UUID;
+import java.util.concurrent.TimeUnit;
 import java.util.stream.Collectors;
 
 import java.lang.ref.WeakReference;
@@ -61,6 +62,8 @@ import javax.annotation.Nullable;
 @Getter
 @Slf4j
 public final class ChatMessage extends SupportMessage {
+    public static final long TTL = TimeUnit.DAYS.toMillis(7);
+
     public interface Listener {
         void onMessageStateChanged();
     }
@@ -339,6 +342,11 @@ public final class ChatMessage extends SupportMessage {
         return resultChatMessage != null && resultChatMessage.getUid().equals(uid);
     }
 
+    @Override
+    public long getTTL() {
+        return TTL;
+    }
+
     private void notifyChangeListener() {
         if (listener != null) {
             Listener listener = this.listener.get();

p2p/src/main/java/bisq/network/p2p/PrefixedSealedAndSignedMessage.java

@@ -26,6 +26,7 @@ import bisq.common.proto.network.NetworkEnvelope;
 import com.google.protobuf.ByteString;
 
 import java.util.UUID;
+import java.util.concurrent.TimeUnit;
 
 import lombok.EqualsAndHashCode;
 import lombok.Value;
@@ -35,6 +36,8 @@ import static com.google.common.base.Preconditions.checkNotNull;
 @EqualsAndHashCode(callSuper = true)
 @Value
 public final class PrefixedSealedAndSignedMessage extends NetworkEnvelope implements MailboxMessage, SendersNodeAddressMessage {
+    public static final long TTL = TimeUnit.DAYS.toMillis(15);
+
     private final NodeAddress senderNodeAddress;
     private final SealedAndSigned sealedAndSigned;
 
@@ -100,4 +103,9 @@ public final class PrefixedSealedAndSignedMessage extends NetworkEnvelope implem
                 proto.getUid(),
                 -1);
     }
+
+    @Override
+    public long getTTL() {
+        return TTL;
+    }
 }

p2p/src/main/java/bisq/network/p2p/mailbox/MailboxMessage.java

@@ -21,7 +21,8 @@ package bisq.network.p2p.mailbox;
 import bisq.network.p2p.DirectMessage;
 import bisq.network.p2p.NodeAddress;
 import bisq.network.p2p.UidMessage;
+import bisq.network.p2p.storage.payload.ExpirablePayload;
 
-public interface MailboxMessage extends DirectMessage, UidMessage {
+public interface MailboxMessage extends DirectMessage, UidMessage, ExpirablePayload {
     NodeAddress getSenderNodeAddress();
 }