diff --git a/libi2pd/SSU2Session.cpp b/libi2pd/SSU2Session.cpp
index cf2eafde..38d52012 100644
--- a/libi2pd/SSU2Session.cpp
+++ b/libi2pd/SSU2Session.cpp
@@ -221,6 +221,7 @@ namespace transport
 			m_IncompleteMessages.clear ();
 			m_RelaySessions.clear ();
 			m_PeerTests.clear ();
+			m_ReceivedI2NPMsgIDs.clear ();
 			m_Server.RemoveSession (m_SourceConnID);
 			transports.PeerDisconnected (shared_from_this ());
 			LogPrint (eLogDebug, "SSU2: Session terminated");
@@ -1450,7 +1451,7 @@ namespace transport
 					nextMsg->len = nextMsg->offset + size + 7; // 7 more bytes for full I2NP header
 					memcpy (nextMsg->GetNTCP2Header (), buf + offset, size);
 					nextMsg->FromNTCP2 (); // SSU2 has the same format as NTCP2
-					m_Handler.PutNextMessage (std::move (nextMsg));
+					HandleI2NPMsg (std::move (nextMsg));
 					m_IsDataReceived = true;
 					break;
 				}
@@ -1738,7 +1739,7 @@ namespace transport
 		{
 			// we have all follow-on fragments already
 			m->msg->FromNTCP2 ();
-			m_Handler.PutNextMessage (std::move (m->msg));
+			HandleI2NPMsg (std::move (m->msg));
 			m_IncompleteMessages.erase (it);
 		}
 	}
@@ -1760,14 +1761,14 @@ namespace transport
 				if (isLast)
 				{
 					it->second->msg->FromNTCP2 ();
-					m_Handler.PutNextMessage (std::move (it->second->msg));
+					HandleI2NPMsg (std::move (it->second->msg));
 					m_IncompleteMessages.erase (it);
 				}
 				else
 				{
 					if (ConcatOutOfSequenceFragments (it->second))
 					{
-						m_Handler.PutNextMessage (std::move (it->second->msg));
+						HandleI2NPMsg (std::move (it->second->msg));
 						m_IncompleteMessages.erase (it);
 					}
 					else
@@ -2268,6 +2269,25 @@ namespace transport
 		}
 	}
 
+	void SSU2Session::HandleI2NPMsg (std::shared_ptr<I2NPMessage>&& msg)
+	{	
+		if (!msg) return;
+		int32_t msgID = msg->GetMsgID ();
+		if (!m_ReceivedI2NPMsgIDs.count (msgID))
+		{	
+			if (!msg->IsExpired ())
+			{
+				// m_LastActivityTimestamp is updated in ProcessData before
+				m_ReceivedI2NPMsgIDs.emplace (msgID, (uint32_t)m_LastActivityTimestamp);
+				m_Handler.PutNextMessage (std::move (msg)); 
+			}
+			else
+				LogPrint (eLogDebug, "SSU2: Message ", msgID, " expired");
+		}	
+		else
+			LogPrint (eLogDebug, "SSU2: Message ", msgID, " already received");
+	}	
+		
 	bool SSU2Session::ExtractEndpoint (const uint8_t * buf, size_t size, boost::asio::ip::udp::endpoint& ep)
 	{
 		if (size < 2) return false;
@@ -2790,6 +2810,20 @@ namespace transport
 			else
 				++it;
 		}
+		if (m_ReceivedI2NPMsgIDs.size () > SSU2_MAX_NUM_RECEIVED_I2NP_MSGIDS || ts > m_LastActivityTimestamp + SSU2_DECAY_INTERVAL)
+			// decay
+			m_ReceivedI2NPMsgIDs.clear ();
+		else
+		{
+			// delete old received msgIDs
+			for (auto it = m_ReceivedI2NPMsgIDs.begin (); it != m_ReceivedI2NPMsgIDs.end ();)
+			{
+				if (ts > it->second + SSU2_RECEIVED_I2NP_MSGIDS_CLEANUP_TIMEOUT)
+					it = m_ReceivedI2NPMsgIDs.erase (it);
+				else
+					++it;
+			}
+		}
 		if (!m_OutOfSequencePackets.empty ())
 		{
 			if (m_OutOfSequencePackets.size () > 2*SSU2_MAX_NUM_ACK_RANGES ||
diff --git a/libi2pd/SSU2Session.h b/libi2pd/SSU2Session.h
index aab02127..b1cc234f 100644
--- a/libi2pd/SSU2Session.h
+++ b/libi2pd/SSU2Session.h
@@ -1,5 +1,5 @@
 /*
-* Copyright (c) 2022, The PurpleI2P Project
+* Copyright (c) 2022-2023, The PurpleI2P Project
 *
 * This file is part of Purple i2pd project and licensed under BSD3
 *
@@ -39,6 +39,9 @@ namespace transport
 	const int SSU2_RESEND_INTERVAL = 300; // in milliseconds
 	const int SSU2_MAX_NUM_RESENDS = 5;
 	const int SSU2_INCOMPLETE_MESSAGES_CLEANUP_TIMEOUT = 30; // in seconds
+	const int SSU2_MAX_NUM_RECEIVED_I2NP_MSGIDS = 5000; // how many msgID we store for duplicates check
+	const int SSU2_RECEIVED_I2NP_MSGIDS_CLEANUP_TIMEOUT = 10; // in seconds
+	const int SSU2_DECAY_INTERVAL = 20; // in seconds
 	const size_t SSU2_MIN_WINDOW_SIZE = 16; // in packets
 	const size_t SSU2_MAX_WINDOW_SIZE = 256; // in packets
 	const size_t SSU2_MIN_RTO = 100; // in milliseconds
@@ -47,7 +50,7 @@ namespace transport
 	const size_t SSU2_MAX_OUTGOING_QUEUE_SIZE = 500; // in messages
 	const int SSU2_MAX_NUM_ACK_RANGES = 32; // to send
 	const uint8_t SSU2_MAX_NUM_FRAGMENTS = 64;
-
+	
 	// flags
 	const uint8_t SSU2_FLAG_IMMEDIATE_ACK_REQUESTED = 0x01;
 
@@ -308,7 +311,8 @@ namespace transport
 			void HandleRelayIntro (const uint8_t * buf, size_t len, int attempts = 0);
 			void HandleRelayResponse (const uint8_t * buf, size_t len);
 			void HandlePeerTest (const uint8_t * buf, size_t len);
-
+			void HandleI2NPMsg (std::shared_ptr<I2NPMessage>&& msg);
+			
 			size_t CreateAddressBlock (uint8_t * buf, size_t len, const boost::asio::ip::udp::endpoint& ep);
 			size_t CreateRouterInfoBlock (uint8_t * buf, size_t len, std::shared_ptr<const i2p::data::RouterInfo> r);
 			size_t CreateAckBlock (uint8_t * buf, size_t len);
@@ -351,6 +355,7 @@ namespace transport
 			SSU2TerminationReason m_TerminationReason;
 			size_t m_MaxPayloadSize;
 			std::unique_ptr<i2p::data::IdentHash> m_PathChallenge;
+			std::unordered_map<uint32_t, uint32_t> m_ReceivedI2NPMsgIDs; // msgID -> timestamp in seconds
 	};
 
 	inline uint64_t CreateHeaderMask (const uint8_t * kh, const uint8_t * nonce)