diff --git a/pymodmilter/config.py b/pymodmilter/config.py
new file mode 100644
index 0000000..2c4a705
--- /dev/null
+++ b/pymodmilter/config.py
@@ -0,0 +1,332 @@
+# PyMod-Milter is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# PyMod-Milter 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 General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with PyMod-Milter.  If not, see <http://www.gnu.org/licenses/>.
+#
+
+__all__ = [
+    "BaseConfig",
+    "ActionConfig",
+    "RuleConfig",
+    "ModifyMilterConfig"]
+
+import json
+import logging
+import re
+
+from bs4 import BeautifulSoup
+from netaddr import IPNetwork, AddrFormatError
+
+
+class BaseConfig:
+    def __init__(self, cfg={}, debug=False):
+        self._cfg = {}
+        if "name" in cfg:
+            assert isinstance(cfg["name"], str), \
+                "rule: name: invalid value, should be string"
+            self["name"] = cfg["name"]
+        else:
+            self["name"] = ""
+
+        if debug:
+            self["loglevel"] = logging.DEBUG
+        elif "loglevel" in cfg:
+            level = getattr(logging, cfg["loglevel"].upper(), None)
+            assert isinstance(level, int), \
+                f"{self['name']}: loglevel: invalid value"
+            self["loglevel"] = level
+        else:
+            self["loglevel"] = logging.INFO
+
+        # the keys/values of args are used as parameters
+        # to functions
+        self["args"] = {}
+
+    def __setitem__(self, key, value):
+        self._cfg[key] = value
+
+    def __getitem__(self, key):
+        return self._cfg[key]
+
+    def __delitem__(self, key):
+        del self._cfg[key]
+
+    def __contains__(self, key):
+        return key in self._cfg
+
+    def add_string_arg(self, cfg, args):
+        if isinstance(args, str):
+            args = [args]
+
+        for arg in args:
+            assert arg in cfg, \
+                f"{self['name']}: mandatory parameter '{arg}' not found"
+            assert isinstance(cfg[arg], str), \
+                f"{self['name']}: {arg}: invalid value, should be string"
+            self["args"][arg] = cfg[arg]
+
+    def add_bool_arg(self, cfg, args):
+        if isinstance(args, str):
+            args = [args]
+
+        for arg in args:
+            assert arg in cfg, \
+                f"{self['name']}: mandatory parameter '{arg}' not found"
+            assert isinstance(cfg[arg], bool), \
+                f"{self['name']}: {arg}: invalid value, should be bool"
+            self["args"][arg] = cfg[arg]
+
+
+class ConditionsConfig(BaseConfig):
+    def __init__(self, parent_cfg, cfg, debug):
+        if "loglevel" not in cfg:
+            cfg["loglevel"] = parent_cfg["loglevel"]
+
+        cfg["name"] = f"{parent_cfg['name']}: condition"
+
+        super().__init__(cfg, debug)
+
+        if "local" in cfg:
+            self.add_bool_arg(cfg, "local")
+
+        if "hosts" in cfg:
+            hosts = cfg["hosts"]
+            assert isinstance(hosts, list) and all(
+                [isinstance(host, str) for host in hosts]), \
+                f"{self['name']}: hosts: invalid value, " \
+                f"should be list of strings"
+
+            self["args"]["hosts"] = []
+            try:
+                for host in cfg["hosts"]:
+                    self["args"]["hosts"].append(IPNetwork(host))
+            except AddrFormatError as e:
+                raise ValueError(f"{self['name']}: hosts: {e}")
+
+        for arg in ("envfrom", "envto"):
+            if arg in cfg:
+                self.add_string_arg(cfg, arg)
+                try:
+                    self["args"][arg] = re.compile(
+                        self["args"][arg],
+                        re.IGNORECASE)
+                except re.error as e:
+                    raise ValueError(f"{self['name']}: {arg}: {e}")
+
+
+class ActionConfig(BaseConfig):
+    def __init__(self, idx, rule_cfg, cfg, debug):
+        if "name" in cfg:
+            cfg["name"] = f"{rule_cfg['name']}: {cfg['name']}"
+        else:
+            cfg["name"] = f"{rule_cfg['name']}: Action #{idx}"
+
+        if "loglevel" not in cfg:
+            cfg["loglevel"] = rule_cfg["loglevel"]
+
+        super().__init__(cfg, debug)
+
+        self["pretend"] = rule_cfg["pretend"]
+        self["conditions"] = None
+        self["type"] = ""
+        self["need_body"] = False
+
+        if "pretend" in cfg:
+            pretend = cfg["pretend"]
+            assert isinstance(pretend, bool), \
+                f"{self['name']}: pretend: invalid value, should be bool"
+            self["pretend"] = pretend
+
+        assert "type" in cfg, \
+            f"{self['name']}: type: invalid value, should be string"
+        assert cfg["type"] in \
+            ("add_header", "del_header", "mod_header", "add_disclaimer",
+             "rewrite_links", "store"), \
+            f"{self['name']}: type: invalid action type"
+        self["type"] = cfg["type"]
+
+        if self["type"] == "add_header":
+            self.add_string_arg(cfg, ("field", "value"))
+
+        elif self["type"] == "mod_header":
+            args = ["field", "value"]
+            if "search" in cfg:
+                args.append("search")
+
+            for arg in args:
+                self.add_string_arg(cfg, arg)
+                if arg in ("field", "search"):
+                    try:
+                        self["args"][arg] = re.compile(
+                            self["args"][arg],
+                            re.MULTILINE + re.DOTALL + re.IGNORECASE)
+                    except re.error as e:
+                        raise ValueError(f"{self['name']}: {arg}: {e}")
+
+        elif self["type"] == "del_header":
+            args = ["field"]
+            if "value" in cfg:
+                args.append("value")
+
+            for arg in args:
+                self.add_string_arg(cfg, arg)
+                try:
+                    self["args"][arg] = re.compile(
+                        self["args"][arg],
+                        re.MULTILINE + re.DOTALL + re.IGNORECASE)
+                except re.error as e:
+                    raise ValueError(f"{self['name']}: {arg}: {e}")
+
+        elif self["type"] == "add_disclaimer":
+            if "error_policy" not in cfg:
+                cfg["error_policy"] = "wrap"
+
+            self.add_string_arg(
+                cfg, ("action", "html_template", "text_template",
+                      "error_policy"))
+            assert self["args"]["action"] in ("append", "prepend"), \
+                f"{self['name']}: action: invalid value, " \
+                f"should be 'append' or 'prepend'"
+            assert self["args"]["error_policy"] in ("wrap",
+                                                    "ignore",
+                                                    "reject"), \
+                f"{self['name']}: error_policy: invalid value, " \
+                f"should be 'wrap', 'ignore' or 'reject'"
+
+            try:
+                with open(self["args"]["html_template"], "r") as f:
+                    html = BeautifulSoup(f.read(), "html.parser")
+                    body = html.find('body')
+                    if body:
+                        # just use content within the body tag if present
+                        html = body
+                    self["args"]["html_template"] = html
+
+                with open(self["args"]["text_template"], "r") as f:
+                    self["args"]["text_template"] = f.read()
+
+            except IOError as e:
+                raise RuntimeError(
+                    f"{self['name']}: unable to open/read template file: {e}")
+
+            self["need_body"] = True
+
+        elif self["type"] == "rewrite_links":
+            self.add_string_arg(cfg, "repl")
+            self["need_body"] = True
+
+        elif self["type"] == "store":
+            self.add_string_arg(cfg, "storage_type")
+            assert self["storage_type"] in ("file"), \
+                f"{self['name']}: storage_type: invalid value, " \
+                f"should be 'file'"
+
+            if self["args"]["storage_type"] == "file":
+                self.add_string_arg(cfg, "directory")
+
+            self["need_body"] = True
+
+
+class RuleConfig(BaseConfig):
+    def __init__(self, idx, milter_cfg, cfg, debug=False):
+        if "name" not in cfg:
+            cfg["name"] = f"Rule #{idx}"
+
+        if "loglevel" not in cfg:
+            cfg["loglevel"] = milter_cfg["loglevel"]
+
+        super().__init__(cfg, debug)
+
+        self["pretend"] = milter_cfg["pretend"]
+        self["conditions"] = None
+        self["actions"] = []
+
+        if "pretend" in cfg:
+            pretend = cfg["pretend"]
+            assert isinstance(pretend, bool), \
+                f"{self['name']}: pretend: invalid value, should be bool"
+            self["pretend"] = pretend
+
+        assert "actions" in cfg, \
+            f"{self['name']}: mandatory parameter 'actions' not found"
+        actions = cfg["actions"]
+        assert isinstance(actions, list), \
+            f"{self['name']}: actions: invalid value, should be list"
+
+        for idx, action_cfg in enumerate(cfg["actions"]):
+            self["actions"].append(
+                ActionConfig(idx, self, action_cfg, debug))
+
+
+class ModifyMilterConfig(BaseConfig):
+    def __init__(self, cfgfile, debug=False):
+        try:
+            with open(cfgfile, "r") as fh:
+                # remove lines with leading # (comments), they
+                # are not allowed in json
+                cfg = re.sub(r"(?m)^\s*#.*\n?", "", fh.read())
+        except IOError as e:
+            raise RuntimeError(f"unable to open/read config file: {e}")
+
+        try:
+            cfg = json.loads(cfg)
+        except json.JSONDecodeError as e:
+            cfg_text = [f"{n+1}: {l}" for n, l in enumerate(cfg.splitlines())]
+            msg = "\n".join(cfg_text)
+            e.msg = f"{msg}\n{e.msg}"
+            raise e
+
+        if "global" in cfg:
+            assert isinstance(cfg["global"], dict), \
+                "global: invalid type, should be dict"
+
+            super().__init__(cfg["global"], debug)
+
+            if "pretend" in cfg["global"]:
+                pretend = cfg["global"]["pretend"]
+                assert isinstance(pretend, bool), \
+                    "global: pretend: invalid value, should be bool"
+                self["pretend"] = pretend
+            else:
+                self["pretend"] = False
+
+            if "socket" in cfg["global"]:
+                socket = cfg["global"]["socket"]
+                assert isinstance(socket, str), \
+                    "global: socket: invalid value, should be string"
+                self["socket"] = socket
+            else:
+                self["socket"] = None
+
+            if "local_addrs" in cfg["global"]:
+                local_addrs = cfg["global"]["local_addrs"]
+                assert isinstance(local_addrs, list) and all(
+                    [isinstance(addr, str) for addr in local_addrs]), \
+                    "global: local_addrs: invalid value, " \
+                    "should be list of strings"
+                self["local_addrs"] = local_addrs
+            else:
+                self["local_addrs"] = [
+                    "::1/128",
+                    "127.0.0.0/8",
+                    "10.0.0.0/8",
+                    "172.16.0.0/12",
+                    "192.168.0.0/16"]
+
+        assert "rules" in cfg, \
+            "mandatory parameter 'rules' not found"
+        assert isinstance(cfg["rules"], list), \
+            "rules: invalid value, should be list"
+
+        self["rules"] = []
+        for idx, rule_cfg in enumerate(cfg["rules"]):
+            self["rules"].append(
+                RuleConfig(idx, self, rule_cfg, debug))