diff --git a/kilter/service/session.py b/kilter/service/session.py
index d296d14aa522374c76c669aa7334e30e6c42dde0..6fd4ecd6ee04c6619f33d065f8707842f4da375c 100644
--- a/kilter/service/session.py
+++ b/kilter/service/session.py
@@ -310,6 +310,7 @@ class Session:
 			match message:
 				case Unknown():
 					if message.content[:len(bname)] == bname:
+						assert isinstance(message.content, memoryview)
 						return message.content
 				# fake buffers for MAIL and RCPT commands
 				case EnvelopeFrom() if name == "MAIL":
@@ -528,12 +529,14 @@ class BodyAccessor(AsyncContextManager[AsyncIterator[memoryview]]):
 			match (await self.session.broadcast.receive()):
 				case Body() as body:
 					try:
+						assert isinstance(body.content, memoryview)
 						yield body.content
 					except GeneratorExit:
 						self.skip = True
 						raise
 				case EndOfMessage() as eom:
 					if not self.skip:
+						assert isinstance(eom.content, memoryview)
 						yield eom.content
 
 	async def write(self, chunk: bytes) -> None:
diff --git a/tests/test_body_accessor.py b/tests/test_body_accessor.py
index c82d925c918358aff42211fc17a9d4e802c83a7d..30cfcd89dcd75bc55dd5ae14dd991a233c8a6ead 100644
--- a/tests/test_body_accessor.py
+++ b/tests/test_body_accessor.py
@@ -1,3 +1,4 @@
+from builtins import memoryview as mv
 from ipaddress import IPv4Address
 from pathlib import Path
 
@@ -36,9 +37,9 @@ class HeaderAccessorTests(AsyncTestCase):
 		async with trio.open_nursery() as tg:
 			tg.start_soon(test_filter)
 			await trio.testing.wait_all_tasks_blocked()
-			await session.deliver(Body(b"Spam, "))
-			await session.deliver(Body(b"spam, "))
-			await session.deliver(EndOfMessage(b"and eggs"))
+			await session.deliver(Body(mv(b"Spam, ")))
+			await session.deliver(Body(mv(b"spam, ")))
+			await session.deliver(EndOfMessage(mv(b"and eggs")))
 
 		assert result == b"Spam, spam, and eggs"
 
@@ -68,10 +69,10 @@ class HeaderAccessorTests(AsyncTestCase):
 		async with trio.open_nursery() as tg:
 			tg.start_soon(test_filter)
 			await trio.testing.wait_all_tasks_blocked()
-			assert Continue == await session.deliver(Body(b"Spam, "))
-			assert Skip == await session.deliver(Body(b"spam, "))
-			assert Skip == await session.deliver(Body(b"spam, "))
-			assert Continue == await session.deliver(EndOfMessage(b"and eggs"))
+			assert Continue == await session.deliver(Body(mv(b"Spam, ")))
+			assert Skip == await session.deliver(Body(mv(b"spam, ")))
+			assert Skip == await session.deliver(Body(mv(b"spam, ")))
+			assert Continue == await session.deliver(EndOfMessage(mv(b"and eggs")))
 
 		assert result1 == b"Spam, "
 		assert result2 == b""
diff --git a/tests/test_header_accessor.py b/tests/test_header_accessor.py
index 00034642c30372b1fc8814f0f45bd35151d92416..902f59f81dbb7319c0acfe23d1db75a54df84f4a 100644
--- a/tests/test_header_accessor.py
+++ b/tests/test_header_accessor.py
@@ -1,3 +1,4 @@
+from builtins import memoryview as mv
 from ipaddress import IPv4Address
 from unittest.mock import call
 
@@ -35,13 +36,13 @@ class HeaderAccessorTests(AsyncTestCase):
 		async with trio.open_nursery() as tg:
 			tg.start_soon(test_filter)
 			await trio.testing.wait_all_tasks_blocked()
-			await session.deliver(Header("Spam", b"spam spam spam"))
-			await session.deliver(Header("Spam", b"spam?"))
-			await session.deliver(Header("Eggs", b"and spam"))
+			await session.deliver(Header("Spam", mv(b"spam spam spam")))
+			await session.deliver(Header("Spam", mv(b"spam?")))
+			await session.deliver(Header("Eggs", mv(b"and spam")))
 			await session.deliver(EndOfHeaders())
 
 			# try and throw the iterator off!
-			await session.deliver(Header("Dead-Parrot", b"and spam"))
+			await session.deliver(Header("Dead-Parrot", mv(b"and spam")))
 
 		assert result == ["Spam", "Spam", "Eggs"]
 
@@ -70,15 +71,15 @@ class HeaderAccessorTests(AsyncTestCase):
 		async with trio.open_nursery() as tg:
 			tg.start_soon(test_filter)
 			await trio.testing.wait_all_tasks_blocked()
-			await session.deliver(Header("Spam", b"spam spam spam"))
-			await session.deliver(Header("Spam", b"spam?"))
-			await session.deliver(Header("Eggs", b"and spam"))
-			await session.deliver(Header("Spam", b"spam spam spam"))
+			await session.deliver(Header("Spam", mv(b"spam spam spam")))
+			await session.deliver(Header("Spam", mv(b"spam?")))
+			await session.deliver(Header("Eggs", mv(b"and spam")))
+			await session.deliver(Header("Spam", mv(b"spam spam spam")))
 			await session.deliver(EndOfHeaders())
 
 			# Try and throw the iterator off!  The filter should not await any further
 			# messages after the EndOfHeaders one.
-			await session.deliver(Header("Dead-Parrot", b"and spam"))
+			await session.deliver(Header("Dead-Parrot", mv(b"and spam")))
 
 		assert result1 == ["Spam", "Spam", "Eggs"]
 		assert result2 == ["Spam", "Spam", "Eggs", "Spam"]
@@ -102,9 +103,9 @@ class HeaderAccessorTests(AsyncTestCase):
 		async with trio.open_nursery() as tg:
 			tg.start_soon(test_filter)
 			await trio.testing.wait_all_tasks_blocked()
-			await session.deliver(Header("Spam", b"spam spam spam"))
-			await session.deliver(Header("Spam", b"spam?"))
-			await session.deliver(Header("Eggs", b"and spam"))
+			await session.deliver(Header("Spam", mv(b"spam spam spam")))
+			await session.deliver(Header("Spam", mv(b"spam?")))
+			await session.deliver(Header("Eggs", mv(b"and spam")))
 			await session.deliver(EndOfHeaders())
 
 		assert result == ["Spam", "Spam", "Eggs"]
@@ -128,9 +129,9 @@ class HeaderAccessorTests(AsyncTestCase):
 		async with trio.open_nursery() as tg:
 			tg.start_soon(test_filter)
 			await trio.testing.wait_all_tasks_blocked()
-			await session.deliver(Header("Spam", b"spam spam spam"))
-			await session.deliver(Header("Spam", b"spam?"))
-			await session.deliver(Header("Eggs", b"and spam"))
+			await session.deliver(Header("Spam", mv(b"spam spam spam")))
+			await session.deliver(Header("Spam", mv(b"spam?")))
+			await session.deliver(Header("Eggs", mv(b"and spam")))
 			await session.deliver(Body(b""))
 
 		assert result == ["Spam", "Spam", "Eggs"]
@@ -151,10 +152,10 @@ class HeaderAccessorTests(AsyncTestCase):
 		async with trio.open_nursery() as tg:
 			tg.start_soon(test_filter)
 			await trio.testing.wait_all_tasks_blocked()
-			await session.deliver(Header("Spam", b"spam spam spam"))
-			await session.deliver(Header("Spam", b"spam?"))
-			await session.deliver(Header("Eggs", b"and spam"))
-			await session.deliver(Header("Ham", b"and spam"))
+			await session.deliver(Header("Spam", mv(b"spam spam spam")))
+			await session.deliver(Header("Spam", mv(b"spam?")))
+			await session.deliver(Header("Eggs", mv(b"and spam")))
+			await session.deliver(Header("Ham", mv(b"and spam")))
 			await session.deliver(EndOfHeaders())
 
 		assert result == ["Spam", "Spam", "Ham"], result
@@ -178,10 +179,10 @@ class HeaderAccessorTests(AsyncTestCase):
 		async with trio.open_nursery() as tg:
 			tg.start_soon(test_filter)
 			await trio.testing.wait_all_tasks_blocked()
-			await session.deliver(Header("Spam", b"spam spam spam"))
-			await session.deliver(Header("Spam", b"spam?"))
-			await session.deliver(Header("Eggs", b"and spam"))
-			await session.deliver(Header("Ham", b"and spam"))
+			await session.deliver(Header("Spam", mv(b"spam spam spam")))
+			await session.deliver(Header("Spam", mv(b"spam?")))
+			await session.deliver(Header("Eggs", mv(b"and spam")))
+			await session.deliver(Header("Ham", mv(b"and spam")))
 			await session.deliver(EndOfHeaders())
 			await session.deliver(EndOfMessage(b""))
 
@@ -210,10 +211,10 @@ class HeaderAccessorTests(AsyncTestCase):
 		async with trio.open_nursery() as tg:
 			tg.start_soon(test_filter)
 			await trio.testing.wait_all_tasks_blocked()
-			await session.deliver(Header("Spam", b"spam spam spam"))
-			await session.deliver(Header("Spam", b"spam?"))
-			await session.deliver(Header("Eggs", b"and spam"))
-			await session.deliver(Header("Ham", b"and spam"))
+			await session.deliver(Header("Spam", mv(b"spam spam spam")))
+			await session.deliver(Header("Spam", mv(b"spam?")))
+			await session.deliver(Header("Eggs", mv(b"and spam")))
+			await session.deliver(Header("Ham", mv(b"and spam")))
 			await session.deliver(EndOfHeaders())
 			await session.deliver(EndOfMessage(b""))
 
@@ -243,8 +244,8 @@ class HeaderAccessorTests(AsyncTestCase):
 		async with trio.open_nursery() as tg:
 			tg.start_soon(test_filter)
 			await trio.testing.wait_all_tasks_blocked()
-			await session.deliver(Header("Spam", b"spam spam spam"))
-			await session.deliver(Header("Eggs", b"and spam"))
+			await session.deliver(Header("Spam", mv(b"spam spam spam")))
+			await session.deliver(Header("Eggs", mv(b"and spam")))
 			await session.deliver(EndOfHeaders())
 			await session.deliver(EndOfMessage(b""))
 
@@ -273,8 +274,8 @@ class HeaderAccessorTests(AsyncTestCase):
 		async with trio.open_nursery() as tg:
 			tg.start_soon(test_filter)
 			await trio.testing.wait_all_tasks_blocked()
-			await session.deliver(Header("Spam", b"spam spam spam"))
-			await session.deliver(Header("Eggs", b"and spam"))
+			await session.deliver(Header("Spam", mv(b"spam spam spam")))
+			await session.deliver(Header("Eggs", mv(b"and spam")))
 			await session.deliver(EndOfHeaders())
 			await session.deliver(EndOfMessage(b""))
 
@@ -306,8 +307,8 @@ class HeaderAccessorTests(AsyncTestCase):
 		async with trio.open_nursery() as tg:
 			tg.start_soon(test_filter)
 			await trio.testing.wait_all_tasks_blocked()
-			await session.deliver(Header("Spam", b"spam spam spam"))
-			await session.deliver(Header("Eggs", b"and spam"))
+			await session.deliver(Header("Spam", mv(b"spam spam spam")))
+			await session.deliver(Header("Eggs", mv(b"and spam")))
 			await session.deliver(EndOfHeaders())
 			await session.deliver(EndOfMessage(b""))
 
@@ -339,8 +340,8 @@ class HeaderAccessorTests(AsyncTestCase):
 		async with trio.open_nursery() as tg:
 			tg.start_soon(test_filter)
 			await trio.testing.wait_all_tasks_blocked()
-			await session.deliver(Header("Spam", b"spam spam spam"))
-			await session.deliver(Header("Eggs", b"and spam"))
+			await session.deliver(Header("Spam", mv(b"spam spam spam")))
+			await session.deliver(Header("Eggs", mv(b"and spam")))
 			await session.deliver(EndOfHeaders())
 			await session.deliver(EndOfMessage(b""))
 
@@ -372,8 +373,8 @@ class HeaderAccessorTests(AsyncTestCase):
 		async with trio.open_nursery() as tg:
 			tg.start_soon(test_filter)
 			await trio.testing.wait_all_tasks_blocked()
-			await session.deliver(Header("Spam", b"spam spam spam"))
-			await session.deliver(Header("Eggs", b"and spam"))
+			await session.deliver(Header("Spam", mv(b"spam spam spam")))
+			await session.deliver(Header("Eggs", mv(b"and spam")))
 			await session.deliver(EndOfHeaders())
 			await session.deliver(EndOfMessage(b""))
 
@@ -409,8 +410,8 @@ class HeaderAccessorTests(AsyncTestCase):
 		async with trio.open_nursery() as tg:
 			tg.start_soon(test_filter)
 			await trio.testing.wait_all_tasks_blocked()
-			await session.deliver(Header("Spam", b"spam spam spam"))
-			await session.deliver(Header("Eggs", b"and spam"))
+			await session.deliver(Header("Spam", mv(b"spam spam spam")))
+			await session.deliver(Header("Eggs", mv(b"and spam")))
 			await session.deliver(EndOfHeaders())
 			await session.deliver(EndOfMessage(b""))
 
@@ -440,8 +441,8 @@ class HeaderAccessorTests(AsyncTestCase):
 		async with trio.open_nursery() as tg:
 			tg.start_soon(test_filter)
 			await trio.testing.wait_all_tasks_blocked()
-			await session.deliver(Header("From", b"test@example.com"))
-			await session.deliver(Header("To", b"test@example.com"))
+			await session.deliver(Header("From", mv(b"test@example.com")))
+			await session.deliver(Header("To", mv(b"test@example.com")))
 			await session.deliver(EndOfHeaders())
 
 	async def test_athrow_type(self) -> None:
@@ -462,8 +463,8 @@ class HeaderAccessorTests(AsyncTestCase):
 		async with trio.open_nursery() as tg:
 			tg.start_soon(test_filter)
 			await trio.testing.wait_all_tasks_blocked()
-			await session.deliver(Header("From", b"test@example.com"))
-			await session.deliver(Header("To", b"test@example.com"))
+			await session.deliver(Header("From", mv(b"test@example.com")))
+			await session.deliver(Header("To", mv(b"test@example.com")))
 			await session.deliver(EndOfHeaders())
 
 	async def test_athrow_type_msg(self) -> None:
@@ -485,8 +486,8 @@ class HeaderAccessorTests(AsyncTestCase):
 		async with trio.open_nursery() as tg:
 			tg.start_soon(test_filter)
 			await trio.testing.wait_all_tasks_blocked()
-			await session.deliver(Header("From", b"test@example.com"))
-			await session.deliver(Header("To", b"test@example.com"))
+			await session.deliver(Header("From", mv(b"test@example.com")))
+			await session.deliver(Header("To", mv(b"test@example.com")))
 			await session.deliver(EndOfHeaders())
 
 	async def test_athrow_inst(self) -> None:
@@ -508,6 +509,6 @@ class HeaderAccessorTests(AsyncTestCase):
 		async with trio.open_nursery() as tg:
 			tg.start_soon(test_filter)
 			await trio.testing.wait_all_tasks_blocked()
-			await session.deliver(Header("From", b"test@example.com"))
-			await session.deliver(Header("To", b"test@example.com"))
+			await session.deliver(Header("From", mv(b"test@example.com")))
+			await session.deliver(Header("To", mv(b"test@example.com")))
 			await session.deliver(EndOfHeaders())
diff --git a/tests/test_session.py b/tests/test_session.py
index 6515ea3a7cf2c5730b63ce07780a53b81e46f622..6503a126152f8e83f01ab69896786223baa33358 100644
--- a/tests/test_session.py
+++ b/tests/test_session.py
@@ -1,3 +1,4 @@
+from builtins import memoryview as mv
 from ipaddress import IPv4Address
 from unittest.mock import call
 
@@ -30,7 +31,7 @@ class SessionTests(AsyncTestCase):
 		await session.deliver(Helo("example.com"))
 		self.assertEqual(session.phase, Phase.MAIL)
 
-		await session.deliver(EnvelopeFrom(b"test@example.com"))
+		await session.deliver(EnvelopeFrom(mv(b"test@example.com")))
 		self.assertEqual(session.phase, Phase.ENVELOPE)
 
 		await session.deliver(Data())
@@ -49,10 +50,10 @@ class SessionTests(AsyncTestCase):
 		session = Session(Connect("example.com", LOCALHOST, 1025), MockEditor())
 		self.assertEqual(session.phase, Phase.CONNECT)
 
-		await session.deliver(EnvelopeRecipient(b"test@example.com", []))
+		await session.deliver(EnvelopeRecipient(mv(b"test@example.com"), []))
 		self.assertEqual(session.phase, Phase.ENVELOPE)
 
-		await session.deliver(Header("To", b"test@example.com"))
+		await session.deliver(Header("To", mv(b"test@example.com")))
 		self.assertEqual(session.phase, Phase.HEADERS)
 
 		await session.deliver(EndOfHeaders())
@@ -75,7 +76,7 @@ class SessionTests(AsyncTestCase):
 			await trio.testing.wait_all_tasks_blocked()
 			await session.deliver(Helo("ham"))
 			assert result == "spam"
-			await session.deliver(EnvelopeFrom(b"eggs"))
+			await session.deliver(EnvelopeFrom(mv(b"eggs")))
 
 		assert result == "eggs"
 
@@ -115,7 +116,7 @@ class SessionTests(AsyncTestCase):
 			tg.start_soon(test_filter)
 			await trio.testing.wait_all_tasks_blocked()
 			await session.deliver(Helo("ham"))
-			await session.deliver(EnvelopeFrom(b"eggs"))
+			await session.deliver(EnvelopeFrom(mv(b"eggs")))
 
 	async def test_await_helo_missing(self) -> None:
 		"""
@@ -132,7 +133,7 @@ class SessionTests(AsyncTestCase):
 		async with trio.open_nursery() as tg:
 			tg.start_soon(test_filter)
 			await trio.testing.wait_all_tasks_blocked()
-			await session.deliver(EnvelopeFrom(b"eggs"))
+			await session.deliver(EnvelopeFrom(mv(b"eggs")))
 
 	async def test_await_mail(self) -> None:
 		"""
@@ -149,7 +150,7 @@ class SessionTests(AsyncTestCase):
 		async with trio.open_nursery() as tg:
 			tg.start_soon(test_filter)
 			await trio.testing.wait_all_tasks_blocked()
-			await session.deliver(EnvelopeFrom(b"eggs"))
+			await session.deliver(EnvelopeFrom(mv(b"eggs")))
 
 		assert result == "eggs"
 
@@ -169,7 +170,7 @@ class SessionTests(AsyncTestCase):
 		async with trio.open_nursery() as tg:
 			tg.start_soon(test_filter)
 			await trio.testing.wait_all_tasks_blocked()
-			await session.deliver(Header("Spam", b"eggs"))
+			await session.deliver(Header("Spam", mv(b"eggs")))
 			await session.deliver(EndOfHeaders())
 
 	async def test_await_from_missing(self) -> None:
@@ -204,9 +205,9 @@ class SessionTests(AsyncTestCase):
 		async with trio.open_nursery() as tg:
 			tg.start_soon(test_filter)
 			await trio.testing.wait_all_tasks_blocked()
-			await session.deliver(EnvelopeRecipient(b"spam", []))
-			await session.deliver(EnvelopeRecipient(b"spam", []))
-			await session.deliver(EnvelopeRecipient(b"eggs", []))
+			await session.deliver(EnvelopeRecipient(mv(b"spam"), []))
+			await session.deliver(EnvelopeRecipient(mv(b"spam"), []))
+			await session.deliver(EnvelopeRecipient(mv(b"eggs"), []))
 			await session.deliver(Data())
 
 		assert result == ["spam", "spam", "eggs"]
@@ -228,7 +229,7 @@ class SessionTests(AsyncTestCase):
 		async with trio.open_nursery() as tg:
 			tg.start_soon(test_filter)
 			await trio.testing.wait_all_tasks_blocked()
-			await session.deliver(Header("Spam", b"eggs"))
+			await session.deliver(Header("Spam", mv(b"eggs")))
 			await session.deliver(EndOfHeaders())
 
 	async def test_await_extension(self) -> None:
@@ -248,11 +249,11 @@ class SessionTests(AsyncTestCase):
 		async with trio.open_nursery() as tg:
 			tg.start_soon(test_filter)
 			await trio.testing.wait_all_tasks_blocked()
-			await session.deliver(Unknown(b"SPAM spam eggs"))
-			await session.deliver(EnvelopeFrom(b"spam", [b"spam", b"eggs"]))
-			await session.deliver(Unknown(b"HAM green eggs"))
-			await session.deliver(EnvelopeRecipient(b"spam", [b"spam", b"eggs"]))
-			await session.deliver(EnvelopeRecipient(b"spam", []))
+			await session.deliver(Unknown(mv(b"SPAM spam eggs")))
+			await session.deliver(EnvelopeFrom(mv(b"spam"), [mv(b"spam"), mv(b"eggs")]))
+			await session.deliver(Unknown(mv(b"HAM green eggs")))
+			await session.deliver(EnvelopeRecipient(mv(b"spam"), [mv(b"spam"), mv(b"eggs")]))
+			await session.deliver(EnvelopeRecipient(mv(b"spam"), []))
 			await session.deliver(Data())
 
 		assert result == [
@@ -278,7 +279,7 @@ class SessionTests(AsyncTestCase):
 		async with trio.open_nursery() as tg:
 			tg.start_soon(test_filter)
 			await trio.testing.wait_all_tasks_blocked()
-			await session.deliver(Header("Spam", b"eggs"))
+			await session.deliver(Header("Spam", mv(b"eggs")))
 			await session.deliver(EndOfHeaders())
 
 	async def test_await_extension_missing(self) -> None:
@@ -390,7 +391,7 @@ class SessionTests(AsyncTestCase):
 			await session.deliver(Macro(Helo.ident, {"{spam}": "yes", "{eggs}": "yes"}))
 			await session.deliver(Helo("test.example.com"))
 			await session.deliver(Macro(Helo.ident, {"{spam}": "no", "{ham}": "maybe"}))
-			await session.deliver(EnvelopeFrom(b"test@example.com"))
+			await session.deliver(EnvelopeFrom(mv(b"test@example.com")))
 
 	async def test_delay(self) -> None:
 		"""
@@ -410,7 +411,7 @@ class SessionTests(AsyncTestCase):
 			await trio.testing.wait_all_tasks_blocked()
 
 			await session.deliver(Helo("test.example.com"))
-			await session.deliver(EnvelopeFrom(b"test@example.com"))
+			await session.deliver(EnvelopeFrom(mv(b"test@example.com")))
 
 	async def test_abort_in_helo(self) -> None:
 		"""