diff --git a/Makefile.autosetup b/Makefile.autosetup
index de1116d2278..8fd1839a766 100644
--- a/Makefile.autosetup
+++ b/Makefile.autosetup
@@ -623,6 +623,21 @@ $(LIBNCRYPT): $(PWD)/ncrypt $(LIBNCRYPTOBJS)
 $(PWD)/ncrypt:
 	$(MKDIR_P) $(PWD)/ncrypt
 
+###############################################################################
+# libnewmail
+@if USE_DEVEL_NEW_MAIL
+LIBNEWMAIL=	libnewmail.a
+LIBNEWMAILOBJS=	newmail/new_mail.o
+CLEANFILES+=	$(LIBNEWMAIL) $(LIBNEWMAILOBJS)
+ALLOBJS+=	$(LIBNEWMAILOBJS)
+
+$(LIBNEWMAIL): $(PWD)/newmail $(LIBNEWMAILOBJS)
+	$(AR) cr $@ $(LIBNEWMAILOBJS)
+	$(RANLIB) $@
+$(PWD)/newmail:
+	$(MKDIR_P) $(PWD)/newmail
+@endif
+
 ###############################################################################
 # libnntp
 LIBNNTP=	libnntp.a
@@ -853,7 +868,7 @@ MUTTLIBS+=	$(LIBINDEX) $(LIBPAGER) $(LIBAUTOCRYPT) $(LIBPOP) \
 		$(LIBNCRYPT) $(LIBIMAP) $(LIBCONN) $(LIBHCACHE) \
 		$(LIBCOMPRESS) $(LIBSIDEBAR) $(LIBBCACHE) $(LIBHISTORY) \
 		$(LIBCORE) $(LIBPARSE) $(LIBCONFIG) $(LIBEMAIL) $(LIBADDRESS) \
-		$(LIBDEBUG) $(LIBMUTT)
+		$(LIBDEBUG) $(LIBNEWMAIL) $(LIBMUTT)
 
 # neomutt
 $(NEOMUTT): $(GENERATED) $(NEOMUTTOBJS) $(MUTTLIBS)
diff --git a/auto.def b/auto.def
index 0ff44676d5b..4df5c6361b0 100644
--- a/auto.def
+++ b/auto.def
@@ -125,6 +125,7 @@ set valid_options {
   debug-notify=0            => "DEBUG: Enable Notifications dump"
   debug-queue=0             => "DEBUG: Enable TAILQ debugging"
   debug-window=0            => "DEBUG: Enable windows dump"
+  devel-new-mail=0          => "Enable new work-in-progress system notifications"
 }
 
 set deprecated_options  {
@@ -168,7 +169,7 @@ if {1} {
   # Keep sorted, please.
   foreach opt {
     asan autocrypt bdb compile-commands coverage debug-backtrace debug-color debug-email
-    debug-graphviz debug-notify debug-queue debug-window doc
+    debug-graphviz devel-new-mail debug-notify debug-queue debug-window doc
     everything fmemopen full-doc fuzzing gdbm gnutls gpgme gsasl gss homespool
     idn2 include-path-in-cflags inotify kyotocabinet lmdb locales-fix lua lz4
     mixmaster nls notmuch pcre2 pgp qdbm rocksdb sasl smime sqlite ssl
@@ -1058,6 +1059,11 @@ if {[get-define want-debug-window]} {
   define USE_DEBUG_WINDOW 1
 }
 
+# WIP notifications implementation
+if {[get-define want-devel-new-mail]} {
+  define USE_DEVEL_NEW_MAIL 1
+}
+
 ###############################################################################
 # Address Sanitizer
 if {[get-define want-asan]} {
diff --git a/core/mailbox.c b/core/mailbox.c
index a55038cd7c0..a69091b31ef 100644
--- a/core/mailbox.c
+++ b/core/mailbox.c
@@ -76,6 +76,10 @@ struct Mailbox *mailbox_new(void)
   m->emails = mutt_mem_calloc(m->email_max, sizeof(struct Email *));
   m->v2r = mutt_mem_calloc(m->email_max, sizeof(int));
   m->gen = mailbox_gen();
+#ifdef USE_DEVEL_NEW_MAIL
+  m->last_notified.tv_sec = 0;
+  m->last_notified.tv_nsec = 0;
+#endif
 
   return m;
 }
diff --git a/core/mailbox.h b/core/mailbox.h
index 613e75c5409..d407c48bd32 100644
--- a/core/mailbox.h
+++ b/core/mailbox.h
@@ -92,6 +92,9 @@ struct Mailbox
   int msg_new;                        ///< Number of new messages
   int msg_deleted;                    ///< Number of deleted messages
   int msg_tagged;                     ///< How many messages are tagged?
+#ifdef USE_DEVEL_NEW_MAIL
+  int msg_unnotified;                 ///< Number of messages we have not notified about
+#endif
 
   struct Email **emails;              ///< Array of Emails
   int email_max;                      ///< Number of pointers in emails
@@ -103,6 +106,9 @@ struct Mailbox
   bool newly_created;                 ///< Mbox or mmdf just popped into existence
   struct timespec mtime;              ///< Time Mailbox was last changed
   struct timespec last_visited;       ///< Time of last exit from this mailbox
+#ifdef USE_DEVEL_NEW_MAIL
+  struct timespec last_notified;      ///< Time when the user was last notified about new messages.
+#endif
 
   const struct MxOps *mx_ops;         ///< MXAPI callback functions
 
@@ -176,6 +182,8 @@ enum NotifyMailbox
   NT_MAILBOX_RESORT,     ///< Email list needs resorting
   NT_MAILBOX_UPDATE,     ///< Update internal tables
   NT_MAILBOX_UNTAG,      ///< Clear the 'last-tagged' pointer
+
+  NT_MAILBOX_NEW_MAIL,   ///< New messages have been added
 };
 
 /**
@@ -183,7 +191,7 @@ enum NotifyMailbox
  */
 struct EventMailbox
 {
-  struct Mailbox *mailbox; ///< The Mailbox this Event relates to
+  struct Mailbox *mailbox;  ///< The Mailbox this Event relates to
 };
 
 void            mailbox_changed   (struct Mailbox *m, enum NotifyMailbox action);
diff --git a/docs/config.c b/docs/config.c
index 0ad4a6a2091..0a9aa2c1e92 100644
--- a/docs/config.c
+++ b/docs/config.c
@@ -1010,6 +1010,19 @@
 ** or when you save it to another folder.
 */
 
+#ifdef USE_DEVEL_NEW_MAIL
+{ "devel_new_mail_command", DT_COMMAND, 0 },
+/*
+** .pp
+** If \fIset\fP, NeoMutt will call this command after a new message is received.
+** The following \fCprintf(3)\fP-like sequences are supported: 
+** .dl 
+** .dt %n  .dd Mailbox name
+** .dt %f  .dd Mailbox folder path
+** .de
+*/
+#endif
+
 { "digest_collapse", DT_BOOL, true },
 /*
 ** .pp
diff --git a/maildir/maildir.c b/maildir/maildir.c
index 0260cd80852..99d263da2c2 100644
--- a/maildir/maildir.c
+++ b/maildir/maildir.c
@@ -46,10 +46,12 @@
 #include <utime.h>
 #include "private.h"
 #include "mutt/lib.h"
+#include "mutt/notify.h"
 #include "config/lib.h"
 #include "email/lib.h"
 #include "core/lib.h"
 #include "lib.h"
+#include "newmail/lib.h"
 #include "progress/lib.h"
 #include "copy.h"
 #include "edata.h"
@@ -95,6 +97,10 @@ static void maildir_check_dir(struct Mailbox *m, const char *dir_name,
   struct Buffer *msgpath = buf_pool_get();
   buf_printf(path, "%s/%s", mailbox_path(m), dir_name);
 
+#ifdef USE_DEVEL_NEW_MAIL
+  bool check_unnotified = check_new;
+#endif
+
   /* when $mail_check_recent is set, if the new/ directory hasn't been modified since
    * the user last exited the m, then we know there is no recent mail.  */
   const bool c_mail_check_recent = cs_subset_bool(NeoMutt->sub, "mail_check_recent");
@@ -136,6 +142,22 @@ static void maildir_check_dir(struct Mailbox *m, const char *dir_name,
     {
       if (check_stats)
         m->msg_unread++;
+
+#ifdef USE_DEVEL_NEW_MAIL
+      if (check_unnotified)
+      {
+        struct timespec created;
+        buf_printf(msgpath, "%s/%s", buf_string(path), de->d_name);
+        stat(buf_string(msgpath), &st);
+        mutt_file_get_stat_timespec(&created, &st, MUTT_STAT_CTIME);
+        if (mutt_file_timespec_compare(&m->last_notified, &created) < 0)
+        {
+          mutt_debug(LL_DEBUG1, "Unnotified %s/%s\n", buf_string(path), de->d_name);
+          m->msg_unnotified++;
+        }
+      }
+#endif
+
       if (check_new)
       {
         if (c_mail_check_recent)
@@ -1361,6 +1383,9 @@ static enum MxStatus maildir_mbox_check_stats(struct Mailbox *m, uint8_t flags)
     m->msg_count = 0;
     m->msg_unread = 0;
     m->msg_flagged = 0;
+#ifdef USE_DEVEL_NEW_MAIL
+    m->msg_unnotified = 0;
+#endif
   }
 
   maildir_check_dir(m, "new", check_new, check_stats);
@@ -1370,6 +1395,17 @@ static enum MxStatus maildir_mbox_check_stats(struct Mailbox *m, uint8_t flags)
   if (check_new || check_stats)
     maildir_check_dir(m, "cur", check_new, check_stats);
 
+#ifdef USE_DEVEL_NEW_MAIL
+  if (check_stats && m->msg_unnotified > 0)
+  {
+    mutt_debug(LL_DEBUG1, "Unnotified = %d\n", m->msg_unnotified);
+    struct EventMailbox ev_m = { m };
+    notify_send(m->notify, NT_MAILBOX, NT_MAILBOX_NEW_MAIL, &ev_m);
+    clock_gettime(CLOCK_REALTIME, &m->last_notified);
+    mutt_debug(LL_DEBUG2, "resetting time\n");
+  }
+#endif
+
   return m->msg_new ? MX_STATUS_NEW_MAIL : MX_STATUS_OK;
 }
 
diff --git a/main.c b/main.c
index 6edcc3620e4..ea455c5c855 100644
--- a/main.c
+++ b/main.c
@@ -159,6 +159,7 @@
 #include "index/lib.h"
 #include "menu/lib.h"
 #include "ncrypt/lib.h"
+#include "newmail/lib.h"
 #include "postpone/lib.h"
 #include "question/lib.h"
 #include "send/lib.h"
@@ -921,6 +922,10 @@ main
   notify_observer_add(NeoMutt->notify, NT_CONFIG, main_log_observer, NULL);
   notify_observer_add(NeoMutt->notify, NT_CONFIG, main_config_observer, NULL);
 
+#ifdef USE_DEVEL_NEW_MAIL
+  notify_observer_add(NeoMutt->notify, NT_MAILBOX, new_mail_observer, NULL);
+#endif
+
   if (sendflags & SEND_POSTPONED)
   {
     if (!OptNoCurses)
diff --git a/mutt_config.c b/mutt_config.c
index 023df14e927..3e9ff81866e 100644
--- a/mutt_config.c
+++ b/mutt_config.c
@@ -371,6 +371,11 @@ static struct ConfigDef MainVars[] = {
   { "new_mail_command", DT_STRING|DT_COMMAND, 0, 0, NULL,
     "External command to run when new mail arrives"
   },
+#ifdef USE_DEVEL_NEW_MAIL
+  { "devel_new_mail_command", DT_STRING|DT_COMMAND, 0, 0, NULL,
+    "External command to run when new mail arrives (in development, clashes with new_mail_command)"
+  },
+#endif
   { "pipe_decode", DT_BOOL, false, 0, NULL,
     "Decode the message when piping it"
   },
diff --git a/mx.c b/mx.c
index 3a29564115f..1b251c26ae7 100644
--- a/mx.c
+++ b/mx.c
@@ -1798,7 +1798,7 @@ int mx_ac_remove(struct Mailbox *m, bool keep_account)
 /**
  * mx_mbox_check_stats - Check the statistics for a mailbox - Wrapper for MxOps::mbox_check_stats()
  *
- * @note Emits: #NT_MAILBOX_CHANGE
+ * @note Emits: #NT_MAILBOX_CHANGE and #NT_MAILBOX_NEW_MAIL
  */
 enum MxStatus mx_mbox_check_stats(struct Mailbox *m, uint8_t flags)
 {
diff --git a/newmail/lib.h b/newmail/lib.h
new file mode 100644
index 00000000000..2a7b03232b3
--- /dev/null
+++ b/newmail/lib.h
@@ -0,0 +1,42 @@
+/**
+ * @file
+ * New mail notification observer.
+ *
+ * @authors
+ * Copyright (C) 2022 Michal Siedlaczek <michal@siedlaczek.me>
+ *
+ * @copyright
+ * This program 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 2 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 General Public License for more
+ * details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef MUTT_NEW_MAIL_H
+#define MUTT_NEW_MAIL_H
+
+#include <stdint.h>
+#include <stdio.h>
+#include "mutt/lib.h"
+#include "format_flags.h"
+
+struct NotifyCallback;
+
+typedef int(Execute)(const char *cmd);
+
+const char *new_mail_format_str(char *buf, size_t buflen, size_t col, int cols,
+                                char op, const char *src, const char *prec,
+                                const char *if_str, const char *else_str,
+                                intptr_t data, MuttFormatFlags flags);
+int handle_new_mail_event(const char *cmd, struct NotifyCallback *nc, Execute *execute);
+int new_mail_observer(struct NotifyCallback *nc);
+
+#endif
diff --git a/newmail/new_mail.c b/newmail/new_mail.c
new file mode 100644
index 00000000000..e572d828444
--- /dev/null
+++ b/newmail/new_mail.c
@@ -0,0 +1,117 @@
+/**
+ * @file
+ * New mail notification observer implementation.
+ *
+ * @authors
+ * Copyright (C) 2022 Michal Siedlaczek <michal@siedlaczek.me>
+ *
+ * @copyright
+ * This program 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 2 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 General Public License for more
+ * details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/**
+ * @page new_mail Notify about new incoming mail
+ *
+ * Use an external command to send a system notification when new mail arrives.
+ */
+
+#include "mutt/lib.h"
+#include "config/lib.h"
+#include "email/lib.h"
+#include "newmail/lib.h"
+#include "mutt_mailbox.h"
+#include "muttlib.h"
+#include "protos.h"
+
+/**
+ * new_mail_format_str - Format a string for the new mail notification.
+ * @param[out] buf      Buffer in which to save string
+ * @param[in]  buflen   Buffer length
+ * @param[in]  col      Starting column
+ * @param[in]  cols     Number of screen columns
+ * @param[in]  op       printf-like operator, e.g. 't'
+ * @param[in]  src      printf-like format string
+ * @param[in]  prec     Field precision, e.g. "-3.4"
+ * @param[in]  if_str   If condition is met, display this string
+ * @param[in]  else_str Otherwise, display this string
+ * @param[in]  data     Private data
+ * @param[in]  flags    Flags, see #MuttFormatFlags
+ * @retval ptr src (unchanged)
+ *
+ * | Expando | Description
+ * | :------ | :-------------------------------------------------------
+ * | \%c     | New messages
+ * | \%n     | Folder name
+ * | \%f     | Folder path
+ * | \%u     | Unread messages
+ */
+const char *new_mail_format_str(char *buf, size_t buflen, size_t col, int cols,
+                                char op, const char *src, const char *prec,
+                                const char *if_str, const char *else_str,
+                                intptr_t data, MuttFormatFlags flags)
+{
+  struct EventMailbox *ev_m = (struct EventMailbox *) data;
+  struct Mailbox *mailbox = ev_m->mailbox;
+
+  switch (op)
+  {
+    case 'n':
+      snprintf(buf, buflen, "%d", mailbox->msg_unnotified);
+      break;
+    case 'N':
+      snprintf(buf, buflen, "%d", mailbox->msg_new);
+      break;
+    case 'f':
+      snprintf(buf, buflen, "%s", NONULL(mailbox_path(mailbox)));
+      break;
+    case 'F':
+      snprintf(buf, buflen, "%s", NONULL(mailbox->name));
+      break;
+    case 'u':
+      snprintf(buf, buflen, "%d", mailbox->msg_unread);
+      break;
+  }
+  return src;
+}
+
+int handle_new_mail_event(const char *cmd, struct NotifyCallback *nc, Execute *execute)
+{
+  if (nc->event_subtype != NT_MAILBOX_NEW_MAIL)
+    return 0;
+
+  struct EventMailbox *ev_m = nc->event_data;
+  if (!ev_m || !ev_m->mailbox)
+    return 0;
+
+  char expanded_cmd[1024];
+  mutt_expando_format(expanded_cmd, 1024, 0, 1024, cmd, new_mail_format_str,
+                      (intptr_t) ev_m, MUTT_FORMAT_NO_FLAGS);
+  execute(expanded_cmd);
+  return 0;
+}
+
+int execute_cmd(const char *cmd)
+{
+  if (mutt_system(cmd) != 0)
+    mutt_error(_("Error running \"%s\""), cmd);
+  return 0;
+}
+
+int new_mail_observer(struct NotifyCallback *nc)
+{
+  const char *c_devel_new_mail_command = cs_subset_string(NeoMutt->sub, "devel_new_mail_command");
+  if (!c_devel_new_mail_command)
+    return 0;
+  return handle_new_mail_event(c_devel_new_mail_command, nc, execute_cmd);
+}
diff --git a/pager/pager.c b/pager/pager.c
index 6d73892ecf0..bcbfe2c311f 100644
--- a/pager/pager.c
+++ b/pager/pager.c
@@ -331,10 +331,8 @@ static int pager_global_observer(struct NotifyCallback *nc)
  */
 static int pager_index_observer(struct NotifyCallback *nc)
 {
-  if (nc->event_type != NT_INDEX)
+  if ((nc->event_type != NT_INDEX) || !nc->global_data)
     return 0;
-  if (!nc->global_data)
-    return -1;
 
   struct MuttWindow *win_pager = nc->global_data;
 
diff --git a/test/Makefile.autosetup b/test/Makefile.autosetup
index de5584b3731..774d537d519 100644
--- a/test/Makefile.autosetup
+++ b/test/Makefile.autosetup
@@ -377,6 +377,11 @@ NEOMUTT_OBJS	= test/neo/neomutt_account_add.o \
 		  test/neo/neomutt_mailboxlist_get_all.o \
 		  test/neo/neomutt_new.o
 
+@if USE_DEVEL_NEW_MAIL
+NEW_MAIL_OBJS	= test/newmail/new_mail_observer.o \
+		  test/newmail/new_mail_format_str.o
+@endif
+
 NOTIFY_OBJS	= test/notify/notify_free.o \
 		  test/notify/notify_new.o \
 		  test/notify/notify_observer_add.o \
@@ -596,7 +601,7 @@ BUILD_DIRS	= $(PWD)/test/account $(PWD)/test/address $(PWD)/test/array \
 		  $(PWD)/test/history $(PWD)/test/idna $(PWD)/test/list \
 		  $(PWD)/test/logging $(PWD)/test/mailbox $(PWD)/test/mapping \
 		  $(PWD)/test/mbyte $(PWD)/test/md5 $(PWD)/test/memory \
-		  $(PWD)/test/neo $(PWD)/test/notify $(PWD)/test/notmuch \
+		  $(PWD)/test/neo $(PWD)/test/newmail $(PWD)/test/notify $(PWD)/test/notmuch \
 		  $(PWD)/test/parameter $(PWD)/test/parse $(PWD)/test/path \
 		  $(PWD)/test/pattern $(PWD)/test/pool $(PWD)/test/prex \
 		  $(PWD)/test/regex $(PWD)/test/rfc2047 $(PWD)/test/rfc2231 \
@@ -659,6 +664,10 @@ TEST_OBJS	= test/main.o test/common.o \
 		  $(THREAD_OBJS) \
 		  $(URL_OBJS)
 
+@if USE_DEVEL_NEW_MAIL
+TEST_OBJS	+= $(NEW_MAIL_OBJS)
+@endif
+
 CFLAGS	+= -I$(SRCDIR)/test
 
 TEST_BINARY = test/neomutt-test$(EXEEXT)
diff --git a/test/main.c b/test/main.c
index 74b9281fa4d..5acf90bd7d4 100644
--- a/test/main.c
+++ b/test/main.c
@@ -634,6 +634,10 @@ NEOMUTT_TEST_LIST
 #ifdef USE_ZSTD
   NEOMUTT_TEST_ITEM(test_compress_zstd)
 #endif
+#ifdef USE_DEVEL_NEW_MAIL
+  NEOMUTT_TEST_ITEM(test_new_mail_observer)
+  NEOMUTT_TEST_ITEM(test_new_mail_format_str)
+#endif
 #if defined(HAVE_BDB) || defined(HAVE_GDBM) || defined(HAVE_KC) || defined(HAVE_LMDB) || defined(HAVE_QDBM) || defined(HAVE_ROCKSDB) || defined(HAVE_TC) || defined(HAVE_TDB)
   NEOMUTT_TEST_ITEM(test_store_store)
 #endif
@@ -686,6 +690,10 @@ NEOMUTT_TEST_ITEM(test_compress_common)
 #ifdef USE_ZSTD
   NEOMUTT_TEST_ITEM(test_compress_zstd)
 #endif
+#ifdef USE_DEVEL_NEW_MAIL
+  NEOMUTT_TEST_ITEM(test_new_mail_observer)
+  NEOMUTT_TEST_ITEM(test_new_mail_format_str)
+#endif
 #if defined(HAVE_BDB) || defined(HAVE_GDBM) || defined(HAVE_KC) || defined(HAVE_LMDB) || defined(HAVE_QDBM) || defined(HAVE_ROCKSDB) || defined(HAVE_TC) || defined(HAVE_TDB)
   NEOMUTT_TEST_ITEM(test_store_store)
 #endif
diff --git a/test/newmail/new_mail_format_str.c b/test/newmail/new_mail_format_str.c
new file mode 100644
index 00000000000..b1b7d0a57c2
--- /dev/null
+++ b/test/newmail/new_mail_format_str.c
@@ -0,0 +1,74 @@
+/**
+ * @file
+ * Test code for new_mail_format_str()
+ *
+ * @authors
+ * Copyright (C) 2022 Michal Siedlaczek <michal@siedlaczek.me>
+ *
+ * @copyright
+ * This program 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 2 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 General Public License for more
+ * details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "mutt/string2.h"
+#define TEST_NO_MAIN
+#include "config.h"
+#include "acutest.h"
+#include "email/lib.h"
+#include "core/lib.h"
+#include "newmail/lib.h"
+
+void test_new_mail_format_str(void)
+{
+  // const char *new_mail_format_str(char *buf, size_t buflen, size_t col, int cols,
+  //                                 char op, const char *src, const char *prec,
+  //                                 const char *if_str, const char *else_str,
+  //                                 intptr_t data, MuttFormatFlags flags);
+
+  char buf[64];
+  size_t col = 0;
+  int cols = 64;
+  struct Mailbox *mailbox = mailbox_new();
+  mailbox->name = mutt_str_dup("MailBox");
+  mailbox->pathbuf = buf_make(16);
+  mailbox->msg_unread = 7;
+  mailbox->msg_unnotified = 2;
+  mailbox->msg_new = 3;
+  buf_strcpy(&mailbox->pathbuf, "/path");
+
+  struct EventMailbox ev_m = { mailbox };
+
+  intptr_t data = (intptr_t) &ev_m;
+
+  new_mail_format_str((char *) buf, 64, col, cols, 'F', NULL, NULL, NULL, NULL, data, 0);
+  TEST_CHECK(mutt_str_equal(buf, "MailBox"));
+  TEST_MSG("Check failed: %s != MailBox", buf);
+
+  new_mail_format_str((char *) buf, 64, col, cols, 'f', NULL, NULL, NULL, NULL, data, 0);
+  TEST_CHECK(mutt_str_equal(buf, "/path"));
+  TEST_MSG("Check failed: %s != /path", buf);
+
+  new_mail_format_str((char *) buf, 64, col, cols, 'u', NULL, NULL, NULL, NULL, data, 0);
+  TEST_CHECK(mutt_str_equal(buf, "7"));
+  TEST_MSG("Check failed: %s != 7", buf);
+
+  new_mail_format_str((char *) buf, 64, col, cols, 'n', NULL, NULL, NULL, NULL, data, 0);
+  TEST_CHECK(mutt_str_equal(buf, "2"));
+  TEST_MSG("Check failed: %s != 2", buf);
+
+  new_mail_format_str((char *) buf, 64, col, cols, 'N', NULL, NULL, NULL, NULL, data, 0);
+  TEST_CHECK(mutt_str_equal(buf, "3"));
+  TEST_MSG("Check failed: %s != 3", buf);
+
+  mailbox_free(&mailbox);
+}
diff --git a/test/newmail/new_mail_observer.c b/test/newmail/new_mail_observer.c
new file mode 100644
index 00000000000..5a35a20bb0d
--- /dev/null
+++ b/test/newmail/new_mail_observer.c
@@ -0,0 +1,64 @@
+/**
+ * @file
+ * Test code for new_mail_observer()
+ *
+ * @authors
+ * Copyright (C) 2022 Michal Siedlaczek <michal@siedlaczek.me>
+ *
+ * @copyright
+ * This program 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 2 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 General Public License for more
+ * details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "mutt/notify.h"
+#include "mutt/observer.h"
+#include "mutt/string2.h"
+#define TEST_NO_MAIN
+#include "config.h"
+#include "acutest.h"
+#include "core/lib.h"
+#include "newmail/lib.h"
+
+static char *message = NULL;
+
+int dummy_execute_cmd(const char *cmd)
+{
+  message = mutt_str_dup(cmd);
+  return 0;
+}
+
+int dummy_new_mail_observer(struct NotifyCallback *nc)
+{
+  return handle_new_mail_event("New messages", nc, dummy_execute_cmd);
+}
+
+void test_new_mail_observer(void)
+{
+  struct Notify *notify = notify_new();
+  notify_observer_add(notify, NT_MAILBOX, dummy_new_mail_observer, NULL);
+  struct Mailbox *mailbox = mailbox_new();
+  mailbox->name = mutt_str_dup("Mailbox");
+  struct EventMailbox event = { mailbox };
+
+  notify_send(notify, NT_MAILBOX, NT_MAILBOX_NEW_MAIL, NULL);
+  TEST_CHECK(message == NULL);
+
+  notify_send(notify, NT_MAILBOX, NT_MAILBOX_NEW_MAIL, &event);
+  TEST_CHECK(message != NULL);
+  TEST_CHECK(mutt_str_equal(message, "New messages"));
+  TEST_MSG("Check failed: \"%s\" != \"New messages\"", message);
+
+  notify_free(&notify);
+  mailbox_free(&mailbox);
+  FREE(&message);
+}
diff --git a/test/pattern/dummy.c b/test/pattern/dummy.c
index e51fa3c9810..4536aa228c1 100644
--- a/test/pattern/dummy.c
+++ b/test/pattern/dummy.c
@@ -26,9 +26,11 @@
 #include <stdint.h>
 #include <stdio.h>
 #include "mutt/lib.h"
+#include "mutt/string2.h"
 #include "core/lib.h"
 #include "history/lib.h"
 #include "menu/lib.h"
+#include "newmail/lib.h"
 #include "mview.h"
 
 struct Address;
@@ -93,16 +95,10 @@ bool OptNoCurses;
 bool OptSearchInvalid;
 bool OptSearchReverse;
 
-typedef uint8_t MuttFormatFlags;
 typedef uint16_t CompletionFlags;
 typedef uint16_t PagerFlags;
 typedef uint8_t SelectFileFlags;
 
-typedef const char *(format_t) (char *buf, size_t buflen, size_t col, int cols,
-                                char op, const char *src, const char *prec,
-                                const char *if_str, const char *else_str,
-                                intptr_t data, MuttFormatFlags flags);
-
 struct Address *alias_reverse_lookup(const struct Address *addr)
 {
   return NULL;
@@ -213,6 +209,7 @@ int mutt_rfc822_write_header(FILE *fp, struct Envelope *env, struct Body *attach
 void mutt_expando_format(char *buf, size_t buflen, size_t col, int cols, const char *src,
                          format_t *callback, intptr_t data, MuttFormatFlags flags)
 {
+  mutt_str_copy(buf, src, buflen);
 }
 
 void menu_pop_current(struct Menu *menu)
diff --git a/version.c b/version.c
index 39ba81527f8..a04f5846996 100644
--- a/version.c
+++ b/version.c
@@ -308,6 +308,9 @@ static struct CompileOptions DebugOpts[] = {
 #ifdef USE_DEBUG_GRAPHVIZ
   { "graphviz", 2 },
 #endif
+#ifdef USE_DEVEL_NEW_MAIL
+  { "new_mail", 2 },
+#endif
 #ifdef USE_DEBUG_NOTIFY
   { "notify", 2 },
 #endif