diff --git a/libervia/backend/plugins/plugin_sec_gre_formatter_mime.py b/libervia/backend/plugins/plugin_sec_gre_formatter_mime.py
new file mode 100644
index 00000000..a3c77046
--- /dev/null
+++ b/libervia/backend/plugins/plugin_sec_gre_formatter_mime.py
@@ -0,0 +1,127 @@
+#!/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/>.
+
+from typing import Final, TYPE_CHECKING, cast
+
+from twisted.words.protocols.jabber import jid
+from twisted.words.protocols.jabber.xmlstream import XMPPHandler
+from twisted.words.xish import domish
+from wokkel import data_form, disco, iwokkel
+from zope.interface import implementer
+
+from libervia.backend.core import exceptions
+from libervia.backend.core.constants import Const as C
+from libervia.backend.core.core_types import SatXMPPEntity
+from libervia.backend.core.i18n import _
+from libervia.backend.core.log import getLogger
+from libervia.backend.plugins.plugin_xep_0106 import XEP_0106
+from .plugin_exp_gre import Formatter
+
+from email.mime.multipart import MIMEMultipart
+from email.mime.text import MIMEText
+
+if TYPE_CHECKING:
+    from libervia.backend.core.main import LiberviaBackend
+
+log = getLogger(__name__)
+
+
+PLUGIN_INFO = {
+    C.PI_NAME: "GRE Formatter: MIME",
+    C.PI_IMPORT_NAME: "GRE-MIME",
+    C.PI_TYPE: "XEP",
+    C.PI_MODES: C.PLUG_MODE_BOTH,
+    C.PI_PROTOCOLS: [],
+    C.PI_DEPENDENCIES: [
+        "GRE",
+    ],
+    C.PI_RECOMMENDATIONS: [],
+    C.PI_MAIN: "GREFormatterMime",
+    C.PI_HANDLER: "yes",
+    C.PI_DESCRIPTION: _("Handle MIME formatting for Gateway Relayed Encryption."),
+}
+
+NS_GRE_MIME: Final = "urn:xmpp:gre:formatter:mime:0"
+
+
+class GREFormatterMime(Formatter):
+    name = "mime"
+    namespace = NS_GRE_MIME
+
+    def __init__(self, host: "LiberviaBackend") -> None:
+        log.info(f"plugin {PLUGIN_INFO[C.PI_NAME]!r} initialization")
+        super().__init__(host)
+        host.register_namespace("gre-mime", NS_GRE_MIME)
+
+    def get_handler(self, client: SatXMPPEntity) -> XMPPHandler:
+        return GREMIMEHandler(self)
+
+    async def format(
+        self,
+        client: SatXMPPEntity,
+        recipient_id: str,
+        message_elt: domish.Element,
+        encryption_data_form: data_form.Form,
+    ) -> bytes:
+        """Format the sent stanza as multipart MIME payload.
+
+        @param client: Client session.
+        @param message_elt: <message> element being sent.
+        @return: MIME formatted payload.
+        """
+        if message_elt.name != "message":
+            raise exceptions.InternalError("Only <message> stanza should be received.")
+
+        try:
+            body = str(next(message_elt.elements(None, "body")))
+        except StopIteration as e:
+            msg = f"Cancelling message sending due to missing body: {message_elt.toXml()}"
+            log.warning(msg)
+            raise exceptions.CancelError(msg) from e
+
+        msg = MIMEMultipart()
+        # "sender_id" is the real email address used by the gateway for this user.
+        msg["From"] = encryption_data_form["sender_id"]
+        msg["To"] = recipient_id
+
+        subject_elt = next(message_elt.elements(None, "subject"), None)
+        if subject_elt:
+            msg["Subject"] = str(subject_elt)
+
+        msg.attach(MIMEText(body))
+
+        return msg.as_bytes()
+
+
+@implementer(iwokkel.IDisco)
+class GREMIMEHandler(XMPPHandler):
+
+    def __init__(self, plugin_parent):
+        self.plugin_parent = plugin_parent
+
+    def getDiscoInfo(
+        self, requestor: jid.JID, target: jid.JID, nodeIdentifier: str = ""
+    ) -> list[disco.DiscoFeature]:
+        return [
+            disco.DiscoFeature(NS_GRE_MIME),
+        ]
+
+    def getDiscoItems(
+        self, requestor: jid.JID, target: jid.JID, nodeIdentifier: str = ""
+    ) -> list[disco.DiscoItems]:
+        return []