diff --git a/chatmaild/src/chatmaild/filtermail.py b/chatmaild/src/chatmaild/filtermail.py
index 0a0a8cdc..056ff66a 100644
--- a/chatmaild/src/chatmaild/filtermail.py
+++ b/chatmaild/src/chatmaild/filtermail.py
@@ -17,7 +17,8 @@ def check_encrypted(message):
     """Check that the message is an OpenPGP-encrypted message."""
     if not message.is_multipart():
         return False
-    if message.get("subject") != "...":
+    subject = message.get("subject")
+    if subject not in ("...", "Encrypted Message"):
         return False
     if message.get_content_type() != "multipart/encrypted":
         return False
diff --git a/chatmaild/src/chatmaild/tests/mail-data/encrypted-k9.eml b/chatmaild/src/chatmaild/tests/mail-data/encrypted-k9.eml
new file mode 100644
index 00000000..7f65ad3e
--- /dev/null
+++ b/chatmaild/src/chatmaild/tests/mail-data/encrypted-k9.eml
@@ -0,0 +1,92 @@
+Date: Mon, 05 Feb 2024 12:22:17 +0100
+From: Jus <tqwertyjd@nine.testrun.org>
+To: REDACTED
+User-Agent: K-9 Mail for Android
+Message-ID: <A238D610-1471-4A32-B387-B07811665F6D@nine.testrun.org>
+Autocrypt: addr=tqwertyjd@nine.testrun.org; keydata=
+ mQGNBGWNXoMBDAC+D3Na6zJX8d8NEIIoYqcGsOeJCtPs4DZIE8x4nVIRewwG6+CU0/Su8J1sdNL8
+ InVYnE0DUnRfL9RpT/6oHPsbuN8Yo/xyZbc6Df0MgstrbkiIpIb6YdpMB9vnS9phpTDXuVXwOdb+
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+ q5OpvQARAQABiQGfBBgBCgAJBYJljV6DApsMAAoJEO02GWHG7wqgwnQL/ijcTiKNO2Cw4pvgggbL
+ 8e2mgXCQn0aNufbYeylGdX/BP2SMRku5OubjESU0oMVx/Hhy19UkUFhCuOeouSNsbTd6w8Ou+nkh
+ 6bs4KJvhMUFVQe6dE8Reci3EoImcTxV9nqWuvhdXkPddht9Pa5PoRpJlpWxHKpMfrPwWtbW/J8qn
+ dnnc+x9FqxLVY+Z75GbrrMI/I2ClvbfgMnOGQxyZRhcPesiaMyp4bYbX3zxrIZXSG68CQERiMXk8
+ UAeZFPgnm4Hh0rP5cn9enn8tj67ruFsEAU3YMi7eOVOSFlamjH0PTVr3ztdoMathEL7n1s5ksk5b
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+ gzMOEa9jSZpfWpiWDYfVYcHqQTOAoyc1ndwJno/4pO+kRmYoIUaoBqNqiqNtnTl9eiJHcb8kuaxa
+ PP5Qy9N6C2QONUAb4aFBPe0cYXQ6AUnOqBmd3w==
+Subject: Encrypted Message
+MIME-Version: 1.0
+Content-Transfer-Encoding: 7bit
+Content-Type: multipart/encrypted; boundary="----GAXGEBIG1Q6UA7H3D91DE8MM3Q54OF";
+  protocol="application/pgp-encrypted"
+
+------GAXGEBIG1Q6UA7H3D91DE8MM3Q54OF
+Content-Type: application/pgp-encrypted
+Content-Transfer-Encoding: quoted-printable
+
+Version: 1
+------GAXGEBIG1Q6UA7H3D91DE8MM3Q54OF
+Content-Type: application/octet-stream; name="encrypted.asc"
+Content-Transfer-Encoding: 7bit
+Content-Disposition: inline; filename="encrypted.asc"
+
+-----BEGIN PGP MESSAGE-----
+
+hQGMAzhWohyp3KpBAQwAp76KkR97c29iXj6XwvYIom2c5jx9tNWBKR4t/oz1ltuh
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+MrxVY64iHOwasTdMu9F+fv8+akI=
+=Dj6B
+-----END PGP MESSAGE-----
+
+------GAXGEBIG1Q6UA7H3D91DE8MM3Q54OF--
diff --git a/chatmaild/src/chatmaild/tests/test_filtermail.py b/chatmaild/src/chatmaild/tests/test_filtermail.py
index 94218448..b8894ad4 100644
--- a/chatmaild/src/chatmaild/tests/test_filtermail.py
+++ b/chatmaild/src/chatmaild/tests/test_filtermail.py
@@ -63,6 +63,17 @@ def test_filtermail_encryption_detection(maildata):
     assert not check_encrypted(msg)
 
 
+def test_filtermail_encryption_detection_k9subject(maildata):
+    msg = maildata(
+        "encrypted-k9.eml", from_addr="1@example.org", to_addr="2@example.org"
+    )
+    assert check_encrypted(msg)
+
+    # if the subject is not "..." it is not considered ac-encrypted
+    msg.replace_header("Subject", "Click this link")
+    assert not check_encrypted(msg)
+
+
 def test_filtermail_is_mdn(maildata, gencreds, handler):
     from_addr = gencreds()[0]
     to_addr = gencreds()[0] + ".other"