diff --git a/libervia/backend/plugins/plugin_sec_autocrypt.py b/libervia/backend/plugins/plugin_sec_autocrypt.py
new file mode 100644
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+++ b/libervia/backend/plugins/plugin_sec_autocrypt.py
@@ -0,0 +1,283 @@
+#!/usr/bin/env python3
+
+# Libervia plugin
+# Copyright (C) 2009-2025 Jérôme Poisson (goffi@goffi.org)
+
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+import base64
+from functools import partial
+from typing import TYPE_CHECKING, cast
+from typing import Literal
+
+from pydantic import BaseModel, field_validator
+from twisted.internet import defer
+from twisted.words.protocols.jabber import jid
+from twisted.words.xish import domish
+
+from libervia.backend.core.constants import Const as C
+from libervia.backend.core.core_types import MessageData, SatXMPPEntity
+from libervia.backend.core.i18n import _
+from libervia.backend.core.log import getLogger
+from libervia.backend.memory import persistent
+from libervia.backend.plugins.plugin_xep_0106 import XEP_0106
+from libervia.backend.plugins.plugin_xep_0131 import XEP_0131
+from libervia.backend.plugins.plugin_xep_0373 import get_gpg_provider
+from libervia.backend.tools.common import regex
+
+if TYPE_CHECKING:
+    from libervia.backend.core.main import LiberviaBackend
+
+log = getLogger(__name__)
+
+
+PLUGIN_INFO = {
+    C.PI_NAME: "Autocrypt",
+    C.PI_IMPORT_NAME: "AUTOCRYPT",
+    C.PI_TYPE: C.PLUG_TYPE_SEC,
+    C.PI_MODES: C.PLUG_MODE_BOTH,
+    C.PI_PROTOCOLS: [],
+    C.PI_DEPENDENCIES: ["XEP-0106", "XEP-0131", "XEP-0373"],
+    C.PI_RECOMMENDATIONS: [],
+    C.PI_MAIN: "Autocrypt",
+    C.PI_HANDLER: "no",
+    C.PI_DESCRIPTION: _(
+        "Autocrypt support, to automatically encrypt message to email gateways when "
+        "suitable."
+    ),
+}
+
+
+class AutocryptHeaderParseError(ValueError):
+    """Raised when Autocrypt header parsing fails"""
+
+
+class AutocryptData(BaseModel):
+    """Parsed Autocrypt header data.
+
+    @param addr: Email address for the key.
+    @param keydata: Base64-encoded public key.
+    @param prefer_encrypt: Encryption preference hint.
+    """
+
+    addr: str
+    keydata: str
+    prefer_encrypt: Literal["mutual"] | None = None
+
+    @field_validator("addr")
+    @classmethod
+    def check_email(cls, value):
+        value = value.strip()
+        if not regex.RE_EMAIL.match(value):
+            raise ValueError("Invalid email address")
+        return value
+
+    @field_validator("keydata")
+    @classmethod
+    def validate_keydata(cls, value: str) -> str:
+        """Validate keydata is proper base64"""
+        try:
+            base64.b64decode(value, validate=True)
+        except ValueError as e:
+            raise ValueError("Invalid base64 in keydata") from e
+        return value.strip()
+
+    def to_header(self) -> str:
+        """Generate the Autocrypt header.
+
+        @return: Formatted header value per Autocrypt specification.
+        """
+        parts = [f"addr={self.addr}", f"keydata={self.keydata}"]
+
+        if self.prefer_encrypt is not None:
+            parts.append(f"prefer-encrypt={self.prefer_encrypt}")
+
+        return "; ".join(parts)
+
+
+def parse_autocrypt_header(header: str) -> AutocryptData:
+    """Parse an Autocrypt header.
+
+    @param header: Raw Autocrypt header value
+    @return: Parsed AutocryptData.
+    @raise AutocryptHeaderParseError: Some required field is invalid or missing.
+    """
+    attributes = {}
+    for part in header.split(";"):
+        part = part.strip()
+        if not part:
+            continue
+        if "=" not in part:
+            # Ignore invalid parts
+            continue
+        key, value = part.split("=", 1)
+        key = key.strip().lower()
+        value = value.strip()
+
+        if key in {"addr", "keydata", "prefer-encrypt"}:
+            attributes[key] = value
+
+    if not attributes.get("addr"):
+        raise AutocryptHeaderParseError('Missing required "addr" attribute')
+    if not attributes.get("keydata"):
+        raise AutocryptHeaderParseError('Missing required "keydata" attribute')
+
+    try:
+        return AutocryptData(
+            addr=attributes["addr"],
+            keydata=attributes["keydata"],
+            prefer_encrypt=attributes.get("prefer-encrypt"),
+        )
+    except ValueError as e:
+        raise AutocryptHeaderParseError(f"Invalid Autocrypt header: {e}") from e
+
+
+class Autocrypt:
+
+    def __init__(self, host: "LiberviaBackend") -> None:
+        self.host = host
+        log.info(f"plugin {PLUGIN_INFO[C.PI_NAME]!r} initialization")
+        self._shim = cast(XEP_0131, host.plugins["XEP-0131"])
+        self._e = cast(XEP_0106, host.plugins["XEP-0106"])
+        host.trigger.add("message_received", self.message_received_trigger)
+        host.trigger.add("sendMessage", self.send_message_trigger)
+
+    def profile_connecting(self, client: SatXMPPEntity) -> None:
+        # Sender already handled.
+        client._autocrypt_seen: set[str] = set()
+        client._autocrypt_gpg_provider = get_gpg_provider(self.host, client)
+
+    async def handle_autocrypt_data(
+        self, client: SatXMPPEntity, mess_data: MessageData, autocrypt_data_raw: str
+    ) -> None:
+        """Process Autocrypt header from XMPP email gateway
+
+        @param client: Client session.
+        @param mess_data: Message data.
+        @param autocrypt_data: Raw Autocrypt header value
+        @raise AutocryptHeaderParseError: For invalid header format
+        """
+        from_jid = mess_data["from"]
+        to_jid = mess_data["to"]
+        is_email_gateway = await self.host.memory.disco.has_identity(
+            client, "gateway", "smtp", jid.JID(to_jid.host)
+        )
+        if to_jid.resource or not is_email_gateway:
+            log.warning("Ignoring Autocrypt header from non email gateway.")
+            return
+
+        try:
+            autocrypt_data = parse_autocrypt_header(autocrypt_data_raw)
+        except AutocryptHeaderParseError as e:
+            log.error(f"Invalid Autocrypt header: {e}")
+            return
+
+        sender_email = self._e.unescape(from_jid.user)
+        if sender_email != autocrypt_data.addr:
+            log.warning(
+                f"Sender email ({sender_email!r}) doesn't match autocrypt header address"
+                f" ({autocrypt_data.addr!r}), ignoring autocrypt data."
+            )
+            return
+
+        if sender_email in client._autocrypt_seen:
+            log.debug(f"We have already handled {sender_email!r} , nothing to do.")
+            return None
+        gpg_provider = client._autocrypt_gpg_provider
+        public_keys = gpg_provider.list_public_keys(sender_email)
+        if not public_keys:
+            log.debug(
+                f"No public key found for {sender_email!r}, importing autocrypt data."
+            )
+            # FIXME: Maybe we should import the Autocrypt key in a separated location?
+            #   Autocrypt is less secure than normal key management.
+            gpg_provider.import_public_key(base64.b64decode(autocrypt_data.keydata))
+        else:
+            log.debug(
+                f"There are already known public key for {sender_email}, we skipt "
+                "autocrypt"
+            )
+        client._autocrypt_seen.add(sender_email)
+
+    def _check_headers(
+        self, client: SatXMPPEntity, mess_data: MessageData
+    ) -> MessageData:
+        try:
+            autocrypt_data = mess_data["extra"]["headers"]["autocrypt"]
+        except KeyError:
+            pass
+        else:
+            defer.ensureDeferred(
+                self.handle_autocrypt_data(client, mess_data, autocrypt_data)
+            )
+        return mess_data
+
+    def message_received_trigger(
+        self,
+        client: SatXMPPEntity,
+        message_elt: domish.Element,
+        post_treat: defer.Deferred,
+    ) -> Literal[True]:
+        post_treat.addCallback(partial(self._check_headers, client))
+        return True
+
+    async def add_autocrypt_header(self, client, mess_data: MessageData) -> MessageData:
+        to_jid = mess_data["to"]
+        if await self.host.memory.disco.has_identity(
+            client, "gateway", "smtp", jid.JID(to_jid.host)
+        ):
+            gpg_provider = client._autocrypt_gpg_provider
+            # FIXME! We currently use from jid as email, but we would need to get sender
+            # email from gateway instead, as we don't know what is actually used, and it
+            # may differ from the JID.
+            sender_email = mess_data["from"].userhost()
+            try:
+                public_key = next(iter(gpg_provider.list_public_keys(sender_email)))
+            except StopIteration:
+                log.debug("No public key found, can't set autocrypt header.")
+                return mess_data
+
+            exported_key = gpg_provider.export_public_key(public_key)
+            autocrypt_data = AutocryptData(
+                addr=sender_email,
+                keydata=base64.b64encode(exported_key).decode("ascii"),
+                prefer_encrypt="mutual",
+            )
+
+            mess_data["extra"].setdefault("headers", {})[
+                "autocrypt"
+            ] = autocrypt_data.to_header()
+        return mess_data
+
+    def send_message_trigger(
+        self, client, mess_data, pre_xml_treatments, post_xml_treatments
+    ) -> Literal[True]:
+        """Process the XEP-0131 related data to be sent"""
+
+        def add_headers(mess_data: MessageData) -> MessageData:
+            extra = mess_data["extra"]
+            self.move_keywords_to_headers(extra)
+            # Now we parse headers, if any.
+            if "headers" in extra:
+                headers_data = HeadersData(**extra["headers"])
+                message_elt = mess_data["xml"]
+                message_elt.addChild(headers_data.to_element())
+            return mess_data
+
+        post_xml_treatments.addCallback(
+            lambda mess_data: defer.ensureDeferred(
+                self.add_autocrypt_header(client, mess_data)
+            )
+        )
+        return True