diff --git a/scripts/mail-check.py b/scripts/mail-check.py
new file mode 100644
index 0000000..47629fb
--- /dev/null
+++ b/scripts/mail-check.py
@@ -0,0 +1,187 @@
+import smtplib, sys
+import argparse
+import os
+import uuid
+import imaplib
+from datetime import datetime, timedelta
+import email
+import time
+
+RETRY = 100
+
+def _send_mail(smtp_host, smtp_port, from_addr, from_pwd, to_addr, subject, starttls):
+    print("Sending mail with subject '{}'".format(subject))
+    message = "\n".join([
+        "From: {from_addr}",
+        "To: {to_addr}",
+        "Subject: {subject}",
+        "",
+        "This validates our mail server can send to Gmail :/"]).format(
+            from_addr=from_addr,
+            to_addr=to_addr,
+            subject=subject)
+
+
+    retry = RETRY
+    while True:
+        with smtplib.SMTP(smtp_host, port=smtp_port) as smtp:
+            if starttls:
+                smtp.starttls()
+            if from_pwd is not None:
+                smtp.login(from_addr, from_pwd)
+            try:
+                smtp.sendmail(from_addr, [to_addr], message)
+                return
+            except smtplib.SMTPResponseException as e:
+                # This is a service unavailable error
+                # In this situation, we want to retry.
+                if e.smtp_code == 451:
+                    if retry > 0:
+                        retry = retry - 1
+                        time.sleep(1)
+                        continue
+                    else:
+                        print("Error while sending mail: %s" % e)
+                        exit(5)
+            except Exception as e:
+                print("Error while sending mail: %s" % e)
+                exit(4)
+
+def _read_mail(
+        imap_host,
+        imap_port,
+        imap_username,
+        to_pwd,
+        subject,
+        ignore_dkim_spf,
+        show_body=False,
+        delete=True):
+    print("Reading mail from %s" % imap_username)
+
+    message = None
+
+    obj = imaplib.IMAP4_SSL(imap_host, imap_port)
+    obj.login(imap_username, to_pwd)
+    obj.select()
+
+    today = datetime.today()
+    cutoff = today - timedelta(days=1)
+    dt = cutoff.strftime('%d-%b-%Y')
+    for _ in range(0, RETRY):
+        print("Retrying")
+        obj.select()
+        typ, data = obj.search(None, '(SINCE %s) (SUBJECT "%s")'%(dt, subject))
+        if data == [b'']:
+            time.sleep(1)
+            continue
+
+        uids = data[0].decode("utf-8").split(" ")
+        if len(uids) != 1:
+          print("Warning: %d messages have been found with subject containing %s " % (len(uids), subject))
+
+        # FIXME: we only consider the first matching message...
+        uid = uids[0]
+        _, raw = obj.fetch(uid, '(RFC822)')
+        if delete:
+            obj.store(uid, '+FLAGS', '\\Deleted')
+            obj.expunge()
+        message = email.message_from_bytes(raw[0][1])
+        print("Message with subject '%s' has been found" % message['subject'])
+        if show_body:
+            for m in message.get_payload():
+                if m.get_content_type() == 'text/plain':
+                    print("Body:\n%s" % m.get_payload(decode=True).decode('utf-8'))
+        break
+
+    if message is None:
+        print("Error: no message with subject '%s' has been found in INBOX of %s" % (subject, imap_username))
+        exit(1)
+
+    if ignore_dkim_spf:
+        return
+
+    # gmail set this standardized header
+    if 'ARC-Authentication-Results' in message:
+        if "dkim=pass" in message['ARC-Authentication-Results']:
+            print("DKIM ok")
+        else:
+            print("Error: no DKIM validation found in message:")
+            print(message.as_string())
+            exit(2)
+        if "spf=pass" in message['ARC-Authentication-Results']:
+            print("SPF ok")
+        else:
+            print("Error: no SPF validation found in message:")
+            print(message.as_string())
+            exit(3)
+    else:
+        print("DKIM and SPF verification failed")
+        exit(4)
+
+def send_and_read(args):
+    src_pwd = None
+    if args.src_password_file is not None:
+        src_pwd = args.src_password_file.readline().rstrip()
+    dst_pwd = args.dst_password_file.readline().rstrip()
+
+    if args.imap_username != '':
+        imap_username = args.imap_username
+    else:
+        imap_username = args.to_addr
+
+    subject = "{}".format(uuid.uuid4())
+
+    _send_mail(smtp_host=args.smtp_host,
+               smtp_port=args.smtp_port,
+               from_addr=args.from_addr,
+               from_pwd=src_pwd,
+               to_addr=args.to_addr,
+               subject=subject,
+               starttls=args.smtp_starttls)
+
+    _read_mail(imap_host=args.imap_host,
+               imap_port=args.imap_port,
+               imap_username=imap_username,
+               to_pwd=dst_pwd,
+               subject=subject,
+               ignore_dkim_spf=args.ignore_dkim_spf)
+
+def read(args):
+    _read_mail(imap_host=args.imap_host,
+               imap_port=args.imap_port,
+               to_addr=args.imap_username,
+               to_pwd=args.imap_password,
+               subject=args.subject,
+               ignore_dkim_spf=args.ignore_dkim_spf,
+               show_body=args.show_body,
+               delete=False)
+
+parser = argparse.ArgumentParser()
+subparsers = parser.add_subparsers()
+
+parser_send_and_read = subparsers.add_parser('send-and-read', description="Send a email with a subject containing a random UUID and then try to read this email from the recipient INBOX.")
+parser_send_and_read.add_argument('--smtp-host', type=str)
+parser_send_and_read.add_argument('--smtp-port', type=str, default=25)
+parser_send_and_read.add_argument('--smtp-starttls', action='store_true')
+parser_send_and_read.add_argument('--from-addr', type=str)
+parser_send_and_read.add_argument('--imap-host', required=True, type=str)
+parser_send_and_read.add_argument('--imap-port', type=str, default=993)
+parser_send_and_read.add_argument('--to-addr', type=str, required=True)
+parser_send_and_read.add_argument('--imap-username', type=str, default='', help="username used for imap login. If not specified, the to-addr value is used")
+parser_send_and_read.add_argument('--src-password-file', type=argparse.FileType('r'))
+parser_send_and_read.add_argument('--dst-password-file', required=True, type=argparse.FileType('r'))
+parser_send_and_read.add_argument('--ignore-dkim-spf', action='store_true', help="to ignore the dkim and spf verification on the read mail")
+parser_send_and_read.set_defaults(func=send_and_read)
+
+parser_read = subparsers.add_parser('read', description="Search for an email with a subject containing 'subject' in the INBOX.")
+parser_read.add_argument('--imap-host', type=str, default="localhost")
+parser_read.add_argument('--imap-port', type=str, default=993)
+parser_read.add_argument('--imap-username', required=True, type=str)
+parser_read.add_argument('--imap-password', required=True, type=str)
+parser_read.add_argument('--ignore-dkim-spf', action='store_true', help="to ignore the dkim and spf verification on the read mail")
+parser_read.add_argument('--show-body', action='store_true', help="print mail text/plain payload")
+parser_read.add_argument('subject', type=str)
+parser_read.set_defaults(func=read)
+
+args = parser.parse_args()
+args.func(args)
diff --git a/tests/default.nix b/tests/default.nix
index 1e1b67b..e78a96f 100644
--- a/tests/default.nix
+++ b/tests/default.nix
@@ -35,6 +35,7 @@ let
     "intern"
     "extern"
     "clamav"
+    "multiple"
   ];
 
   # Generate an attribute set containing one test per releases
diff --git a/tests/multiple.nix b/tests/multiple.nix
new file mode 100644
index 0000000..c6a4edf
--- /dev/null
+++ b/tests/multiple.nix
@@ -0,0 +1,87 @@
+# This tests is used to test features requiring several mail domains.
+
+{ pkgs ? import <nixpkgs> {}}:
+
+let
+    hashPassword = password: pkgs.runCommand
+      "password-${password}-hashed"
+      { buildInputs = [ pkgs.mkpasswd ]; }
+      ''
+        mkpasswd -m sha-512 ${password} > $out
+      '';
+
+    password = pkgs.writeText "password" "password";
+
+    domainGenerator = domain: { config, pkgs, ... }: {
+      imports = [../default.nix];
+      virtualisation.memorySize = 1024;
+      mailserver = {
+        enable = true;
+        fqdn = "mail.${domain}";
+        domains = [ domain ];
+        localDnsResolver = false;
+        loginAccounts = {
+          "user@${domain}" = {
+            hashedPasswordFile = hashPassword "password";
+          };
+        };
+        enableImap = true;
+        enableImapSsl = true;
+      };
+      services.dnsmasq = {
+        enable = true;
+        extraConfig = ''
+          mx-host=domain1.com,domain1,10
+          mx-host=domain2.com,domain2,10
+        '';
+      };
+    };
+
+in
+
+pkgs.nixosTest {
+  name = "multiple";
+  nodes = {
+    domain1 = {...}: {
+      imports = [
+        ../default.nix
+        (domainGenerator "domain1.com")
+      ];
+      mailserver.forwards = {
+        "non-local@domain1.com" = ["user@domain2.com" "user@domain1.com"];
+        "non@domain1.com" = ["user@domain2.com" "user@domain1.com"];
+      };
+    };
+    domain2 = domainGenerator "domain2.com";
+    client = { config, pkgs, ... }: {
+      environment.systemPackages = [
+        (pkgs.writeScriptBin "mail-check" ''
+          ${pkgs.python3}/bin/python ${../scripts/mail-check.py} $@
+        '')];
+    };
+  };
+  testScript = ''
+    start_all()
+
+    domain1.wait_for_unit("multi-user.target")
+    domain2.wait_for_unit("multi-user.target")
+
+    # TODO put this blocking into the systemd units?
+    domain1.wait_until_succeeds(
+        "timeout 1 ${pkgs.netcat}/bin/nc -U /run/rspamd/rspamd-milter.sock < /dev/null; [ $? -eq 124 ]"
+    )
+    domain2.wait_until_succeeds(
+        "timeout 1 ${pkgs.netcat}/bin/nc -U /run/rspamd/rspamd-milter.sock < /dev/null; [ $? -eq 124 ]"
+    )
+
+    # user@domain1.com sends a mail to user@domain2.com
+    client.succeed(
+        "mail-check send-and-read --smtp-port 587 --smtp-starttls --smtp-host domain1 --from-addr user@domain1.com --imap-host domain2 --to-addr user@domain2.com --src-password-file ${password} --dst-password-file ${password} --ignore-dkim-spf"
+    )
+
+    # Send a mail to the address forwarded and check it is in the recipient mailbox
+    client.succeed(
+        "mail-check send-and-read --smtp-port 587 --smtp-starttls --smtp-host domain1 --from-addr user@domain1.com --imap-host domain2 --to-addr non-local@domain1.com --imap-username user@domain2.com --src-password-file ${password} --dst-password-file ${password} --ignore-dkim-spf"
+    )
+  '';
+}