diff --git a/endpoints/misc.py b/endpoints/misc.py
index 9a8dcf0..c8e1211 100644
--- a/endpoints/misc.py
+++ b/endpoints/misc.py
@@ -12,7 +12,7 @@
 
 from orm import DB
 from services import Service
-from tools import formats
+from tools import formats, mconf
 from tools.tasq import TasQServer
 
 
@@ -152,3 +152,19 @@ def getDisabledPluginsOfUser():
     disabledPlugins = [p[0] for p in disabledPlugins]
 
     return jsonify({ "data": disabledPlugins })
+
+
+@API.route(api.BaseRoute+"/oofSubjectPrefix", methods=["GET"])
+@secure(requireAuth=False)
+def getOofSubjectPrefix():
+    """Report the gromox.cfg autoreply_subject_prefix directive.
+
+    A client offering an out-of-office form needs it to tell the user what an
+    empty subject will send. An unset directive is reported as
+    configured=false rather than guessed at, because the default that then
+    applies is compiled into the running gromox build.
+    """
+    prefix, error = mconf.readGromoxDirective("autoreply_subject_prefix")
+    if error is not None:
+        return jsonify(message=error), 500
+    return jsonify({"data": {"prefix": prefix, "configured": prefix is not None}})
diff --git a/res/openapi.yaml b/res/openapi.yaml
index 857b442..c39e754 100644
--- a/res/openapi.yaml
+++ b/res/openapi.yaml
@@ -2293,6 +2293,41 @@ paths:
         '503':
           $ref: '#/components/responses/DatabaseError'
 
+  /oofSubjectPrefix:
+    get:
+      summary: Get the configured out-of-office reply subject prefix
+      description: >
+        Reports the gromox.cfg autoreply_subject_prefix directive, which gromox
+        prepends to the subject of the incoming message when a mailbox has no
+        out-of-office subject of its own. Clients offering an out-of-office form
+        use it to show what an empty subject will send.
+      operationId: oofSubjectPrefix
+      tags:
+        - Misc
+      responses:
+        '200':
+          description: Prefix state returned
+          content:
+            application/json:
+              schema:
+                type: object
+                properties:
+                  data:
+                    type: object
+                    properties:
+                      prefix:
+                        type: string
+                        nullable: true
+                        description: The configured prefix, or null when the directive is not set
+                      configured:
+                        type: boolean
+                        description: >
+                          Whether the directive is set. When false, gromox applies the
+                          default compiled into the running build, which cannot be read
+                          from the configuration file.
+        '500':
+          $ref: '#/components/responses/ServerError'
+
   /domains/{domainID}/users:
     get:
       summary: Get lists of users
diff --git a/tools/config.py b/tools/config.py
index 41ad2ae..1a86778 100644
--- a/tools/config.py
+++ b/tools/config.py
@@ -96,7 +96,8 @@ def _defaultConfig():
             },
         "mconf": {
           "ldapPath": "/etc/gromox/ldap_adaptor.cfg",
-          "authmgrPath": "/etc/gromox/authmgr.cfg"
+          "authmgrPath": "/etc/gromox/authmgr.cfg",
+          "gromoxPath": "/etc/gromox/gromox.cfg"
           },
         "logs": {},
         "sync": {
diff --git a/tools/mconf.py b/tools/mconf.py
index f612ada..1a64525 100644
--- a/tools/mconf.py
+++ b/tools/mconf.py
@@ -9,6 +9,8 @@
 from .misc import setDirectoryOwner, setDirectoryPermission
 from services import Service
 
+from os.path import exists
+
 import logging
 logger = logging.getLogger("mconf")
 
@@ -235,6 +237,32 @@ def dumpAuthmgr(conf=None, file=None, reloadServices=False):
 ###############################################################################
 
 
+def readGromoxDirective(name):
+    """Read a single directive from the main gromox configuration file.
+
+    Not cached, so an admin editing gromox.cfg need not restart the API.
+    gromox trims trailing whitespace off every configuration line and
+    _loadConf does too, so this returns the value gromox itself sees.
+
+    Returns
+    -------
+    tuple
+        (value, error). value is None when the directive is not set.
+    """
+    if "gromoxPath" not in Config["mconf"]:
+        return None, "mconf.gromoxPath not set"
+    path = Config["mconf"]["gromoxPath"]
+    if not exists(path):
+        return None, "'{}' does not exist".format(path)
+    try:
+        return _loadConf(path).get(name), None
+    except Exception as err:
+        return None, " - ".join((str(arg) for arg in err.args))
+
+
+###############################################################################
+
+
 def load():
     error = loadLdap()
     if error: