diff -ruN core-2.3.20-original/configure.ac core-2.3.20/configure.ac
--- core-2.3.20-original/configure.ac	2022-12-19 12:38:16.000000000 +0300
+++ core-2.3.20/configure.ac	2023-02-09 11:22:36.282856675 +0300
@@ -92,6 +92,22 @@
   TEST_WITH(libunwind, $withval),
   want_libunwind=auto)
 
+AC_ARG_WITH(vpopmail,
+AS_HELP_STRING([--with-vpopmail], [Build with vpopmail support (auto)]),
+	if test x$withval = xno; then
+		want_vpopmail=no
+	else
+		if test x$withval = xyes || test x$withval = xauto; then
+			vpopmail_home="`echo ~vpopmail`"
+			want_vpopmail=$withval
+		else
+			vpopmail_home="$withval"
+			want_vpopmail=yes
+		fi
+	fi, [
+		want_vpopmail=no
+	])
+
 # Berkeley DB support is more or less broken. Disabled for now.
 #AC_ARG_WITH(db,
 #AS_HELP_STRING([--with-db], [Build with Berkeley DB support]),
@@ -556,6 +572,7 @@
 DOVECOT_WANT_SODIUM
 DOVECOT_WANT_SQLITE
 DOVECOT_WANT_CASSANDRA
+DOVECOT_WANT_VPOPMAIL
 
 DOVECOT_SQL
 
diff -ruN core-2.3.20-original/doc/example-config/conf.d/10-auth.conf core-2.3.20/doc/example-config/conf.d/10-auth.conf
--- core-2.3.20-original/doc/example-config/conf.d/10-auth.conf	2022-12-19 12:38:16.000000000 +0300
+++ core-2.3.20/doc/example-config/conf.d/10-auth.conf	2023-02-09 11:22:36.282856675 +0300
@@ -10,7 +10,7 @@
 #disable_plaintext_auth = yes
 
 # Authentication cache size (e.g. 10M). 0 means it's disabled. Note that
-# bsdauth and PAM require cache_key to be set for caching to be used.
+# bsdauth, PAM and vpopmail require cache_key to be set for caching to be used.
 #auth_cache_size = 0
 # Time to live for cached data. After TTL expires the cached record is no
 # longer used, *except* if the main database lookup returns internal failure.
@@ -124,4 +124,5 @@
 #!include auth-ldap.conf.ext
 #!include auth-passwdfile.conf.ext
 #!include auth-checkpassword.conf.ext
+#!include auth-vpopmail.conf.ext
 #!include auth-static.conf.ext
diff -ruN core-2.3.20-original/doc/example-config/conf.d/auth-vpopmail.conf.ext core-2.3.20/doc/example-config/conf.d/auth-vpopmail.conf.ext
--- core-2.3.20-original/doc/example-config/conf.d/auth-vpopmail.conf.ext	1970-01-01 02:00:00.000000000 +0200
+++ core-2.3.20/doc/example-config/conf.d/auth-vpopmail.conf.ext	2023-02-09 11:22:36.282856675 +0300
@@ -0,0 +1,17 @@
+# Authentication for vpopmail users. Included from 10-auth.conf.
+#
+# <doc/wiki/AuthDatabase.VPopMail.txt>
+
+passdb {
+  driver = vpopmail
+
+  # [cache_key=<key>] [webmail=<ip>]
+  args =
+}
+
+userdb {
+  driver = vpopmail
+
+  # [quota_template=<template>] - %q expands to Maildir++ quota
+  args = quota_template=quota_rule=*:backend=%q
+}
diff -ruN core-2.3.20-original/doc/example-config/conf.d/Makefile.am core-2.3.20/doc/example-config/conf.d/Makefile.am
--- core-2.3.20-original/doc/example-config/conf.d/Makefile.am	2022-12-19 12:38:16.000000000 +0300
+++ core-2.3.20/doc/example-config/conf.d/Makefile.am	2023-02-09 11:22:36.282856675 +0300
@@ -11,6 +11,7 @@
 	auth-sql.conf.ext \
 	auth-static.conf.ext \
 	auth-system.conf.ext \
+	auth-vpopmail.conf.ext \
 	10-auth.conf \
 	10-director.conf \
 	10-logging.conf \
diff -ruN core-2.3.20-original/m4/want_vpopmail.m4 core-2.3.20/m4/want_vpopmail.m4
--- core-2.3.20-original/m4/want_vpopmail.m4	1970-01-01 02:00:00.000000000 +0200
+++ core-2.3.20/m4/want_vpopmail.m4	2023-02-09 11:22:36.282856675 +0300
@@ -0,0 +1,33 @@
+AC_DEFUN([DOVECOT_WANT_VPOPMAIL], [
+  have_vpopmail=no
+  if test $want_vpopmail != no; then
+          vpop_etc="$vpopmail_home/etc"
+          AC_MSG_CHECKING([for vpopmail configuration at $vpop_etc/lib_deps])
+          if ! test -f $vpop_etc/lib_deps; then
+                  AC_MSG_RESULT(not found)
+                  vpop_etc="$vpopmail_home"
+                  AC_MSG_CHECKING([for vpopmail configuration at $vpop_etc/lib_deps])
+          fi
+          if test -f $vpop_etc/lib_deps; then
+                  AUTH_CFLAGS="$AUTH_CFLAGS `cat $vpop_etc/inc_deps` $CFLAGS"
+                  AUTH_LIBS="$AUTH_LIBS `cat $vpop_etc/lib_deps`"
+                  AC_DEFINE(USERDB_VPOPMAIL,, [Build with vpopmail support])
+                  AC_DEFINE(PASSDB_VPOPMAIL,, [Build with vpopmail support])
+                  AC_MSG_RESULT(found)
+                  have_vpopmail=yes
+          else
+                  AC_MSG_RESULT(not found)
+                  if test $want_vpopmail = yes; then
+                    AC_ERROR([Can't build with vpopmail support: $vpop_etc/lib_deps not found])
+                  fi
+          fi
+  fi
+  
+  if test $have_vpopmail = no; then
+    not_passdb="$not_passdb vpopmail"
+    not_userdb="$not_userdb vpopmail"
+  else
+    userdb="$userdb vpopmail"
+    passdb="$passdb vpopmail"
+  fi
+])
diff -ruN core-2.3.20-original/src/auth/db-checkpassword.c core-2.3.20/src/auth/db-checkpassword.c
--- core-2.3.20-original/src/auth/db-checkpassword.c	2022-12-19 12:38:16.000000000 +0300
+++ core-2.3.20/src/auth/db-checkpassword.c	2023-02-09 11:22:36.282856675 +0300
@@ -116,8 +116,20 @@
 checkpassword_request_finish_auth(struct chkpw_auth_request *request)
 {
 	switch (request->exit_status) {
+	/* vpopmail exit codes: */
+	case 3:		/* password fail / vpopmail user not found */
+	case 12: 	/* null user name given */
+	case 13:	/* null password given */
+	case 15:	/* user has no password */
+	case 20:	/* invalid user/domain characters */
+	case 21:	/* system user not found */
+	case 22:	/* system user shadow entry not found */
+	case 23:	/* system password fail */
+
 	/* standard checkpassword exit codes: */
 	case 1:
+		/* (1 is additionally defined in vpopmail for
+		   "pop/smtp/webmail/ imap/access denied") */
 		e_info(authdb_event(request->request),
 		       "Login failed (status=%d)",
 		       request->exit_status);
diff -ruN core-2.3.20-original/src/auth/Makefile.am core-2.3.20/src/auth/Makefile.am
--- core-2.3.20-original/src/auth/Makefile.am	2022-12-19 12:38:16.000000000 +0300
+++ core-2.3.20/src/auth/Makefile.am	2023-02-09 11:22:36.282856675 +0300
@@ -139,6 +139,7 @@
 	passdb-passwd-file.c \
 	passdb-pam.c \
 	passdb-shadow.c \
+	passdb-vpopmail.c \
 	passdb-sql.c \
 	passdb-static.c \
 	passdb-template.c \
@@ -150,6 +151,7 @@
 	userdb-passwd-file.c \
 	userdb-prefetch.c \
 	userdb-static.c \
+	userdb-vpopmail.c \
 	userdb-sql.c \
 	userdb-template.c \
 	$(ldap_sources) \
@@ -193,7 +195,8 @@
 	password-scheme.h \
 	userdb.h \
 	userdb-blocking.h \
-	userdb-template.h
+	userdb-template.h \
+	userdb-vpopmail.h
 
 if GSSAPI_PLUGIN
 libmech_gssapi_la_LDFLAGS = -module -avoid-version
diff -ruN core-2.3.20-original/src/auth/passdb.c core-2.3.20/src/auth/passdb.c
--- core-2.3.20-original/src/auth/passdb.c	2022-12-19 12:38:16.000000000 +0300
+++ core-2.3.20/src/auth/passdb.c	2023-02-09 11:22:36.282856675 +0300
@@ -319,6 +319,7 @@
 extern struct passdb_module_interface passdb_passwd_file;
 extern struct passdb_module_interface passdb_pam;
 extern struct passdb_module_interface passdb_checkpassword;
+extern struct passdb_module_interface passdb_vpopmail;
 extern struct passdb_module_interface passdb_ldap;
 extern struct passdb_module_interface passdb_sql;
 extern struct passdb_module_interface passdb_static;
@@ -338,6 +339,7 @@
 	passdb_register_module(&passdb_pam);
 	passdb_register_module(&passdb_checkpassword);
 	passdb_register_module(&passdb_shadow);
+	passdb_register_module(&passdb_vpopmail);
 	passdb_register_module(&passdb_ldap);
 	passdb_register_module(&passdb_sql);
 	passdb_register_module(&passdb_static);
diff -ruN core-2.3.20-original/src/auth/passdb-vpopmail.c core-2.3.20/src/auth/passdb-vpopmail.c
--- core-2.3.20-original/src/auth/passdb-vpopmail.c	1970-01-01 02:00:00.000000000 +0200
+++ core-2.3.20/src/auth/passdb-vpopmail.c	2023-02-09 11:22:36.282856675 +0300
@@ -0,0 +1,229 @@
+/* Copyright (c) 2002-2018 Dovecot authors, see the included COPYING file */
+
+/* Thanks to Courier-IMAP for showing how the vpopmail API should be used */
+
+#include "auth-common.h"
+#include "passdb.h"
+
+#ifdef PASSDB_VPOPMAIL
+
+#include "safe-memset.h"
+#include "password-scheme.h"
+#include "auth-cache.h"
+
+#include "userdb-vpopmail.h"
+
+
+#define VPOPMAIL_DEFAULT_PASS_SCHEME "CRYPT"
+
+/* pw_flags was added in vpopmail 5.4, olders use pw_gid field */
+#ifndef VQPASSWD_HAS_PW_FLAGS
+#  define pw_flags pw_gid
+#endif
+
+struct vpopmail_passdb_module {
+	struct passdb_module module;
+
+	struct ip_addr webmail_ip;
+};
+
+static bool vpopmail_is_disabled(struct auth_request *request,
+				 const struct vqpasswd *vpw)
+{
+        struct passdb_module *_module = request->passdb->passdb;
+	struct vpopmail_passdb_module *module =
+		(struct vpopmail_passdb_module *)_module;
+
+	if (strcasecmp(request->fields.service, "IMAP") == 0) {
+		if ((vpw->pw_flags & NO_IMAP) != 0) {
+			/* IMAP from webmail IP may still be allowed */
+			if (!net_ip_compare(&module->webmail_ip,
+					    &request->fields.remote_ip))
+				return TRUE;
+		}
+		if ((vpw->pw_flags & NO_WEBMAIL) != 0) {
+			if (net_ip_compare(&module->webmail_ip,
+					   &request->fields.remote_ip))
+				return TRUE;
+		}
+	}
+	if ((vpw->pw_flags & NO_POP) != 0 &&
+	    strcasecmp(request->fields.service, "POP3") == 0)
+		return TRUE;
+	if ((vpw->pw_flags & NO_SMTP) != 0 &&
+	    strcasecmp(request->fields.service, "SMTP") == 0)
+		return TRUE;
+	return FALSE;
+}
+
+static char *
+vpopmail_password_lookup(struct auth_request *auth_request, bool *cleartext,
+			 enum passdb_result *result_r)
+{
+	char vpop_user[VPOPMAIL_LIMIT], vpop_domain[VPOPMAIL_LIMIT];
+	struct vqpasswd *vpw;
+	char *password;
+
+	vpw = vpopmail_lookup_vqp(auth_request, vpop_user, vpop_domain);
+	if (vpw == NULL) {
+		*result_r = PASSDB_RESULT_USER_UNKNOWN;
+		return NULL;
+	}
+
+	if (vpopmail_is_disabled(auth_request, vpw)) {
+		e_info(authdb_event(auth_request),
+		       "%s disabled in vpopmail for this user",
+		       auth_request->fields.service);
+		password = NULL;
+		*result_r = PASSDB_RESULT_USER_DISABLED;
+	} else {
+		if (vpw->pw_clear_passwd != NULL &&
+		    *vpw->pw_clear_passwd != '\0') {
+			password = t_strdup_noconst(vpw->pw_clear_passwd);
+			*cleartext = TRUE;
+		} else if (!*cleartext)
+			password = t_strdup_noconst(vpw->pw_passwd);
+		else
+			password = NULL;
+		*result_r = password != NULL ? PASSDB_RESULT_OK :
+			PASSDB_RESULT_SCHEME_NOT_AVAILABLE;
+	}
+
+	safe_memset(vpw->pw_passwd, 0, strlen(vpw->pw_passwd));
+	if (vpw->pw_clear_passwd != NULL) {
+		safe_memset(vpw->pw_clear_passwd, 0,
+			    strlen(vpw->pw_clear_passwd));
+	}
+
+	return password;
+}
+
+static void vpopmail_lookup_credentials(struct auth_request *request,
+					lookup_credentials_callback_t *callback)
+{
+	enum passdb_result result;
+	char *password;
+	bool cleartext = TRUE;
+
+	password = vpopmail_password_lookup(request, &cleartext, &result);
+	if (password == NULL) {
+		callback(result, NULL, 0, request);
+		return;
+	}
+	
+	passdb_handle_credentials(PASSDB_RESULT_OK, password, "CLEARTEXT",
+				  callback, request);
+	safe_memset(password, 0, strlen(password));
+}
+
+static void
+vpopmail_verify_plain(struct auth_request *request, const char *password,
+		      verify_plain_callback_t *callback)
+{
+	enum passdb_result result;
+	const char *scheme, *tmp_pass;
+	char *crypted_pass;
+	bool cleartext = FALSE;
+	int ret;
+
+	crypted_pass = vpopmail_password_lookup(request, &cleartext, &result);
+	if (crypted_pass == NULL) {
+		callback(result, request);
+		return;
+	}
+	tmp_pass = crypted_pass;
+
+	if (cleartext)
+		scheme = "CLEARTEXT";
+	else {
+		scheme = password_get_scheme(&tmp_pass);
+		if (scheme == NULL)
+			scheme = request->passdb->passdb->default_pass_scheme;
+	}
+
+	ret = auth_request_password_verify(request, password, tmp_pass,
+					   scheme, AUTH_SUBSYS_DB);
+	safe_memset(crypted_pass, 0, strlen(crypted_pass));
+
+	if (ret <= 0) {
+		callback(PASSDB_RESULT_PASSWORD_MISMATCH, request);
+		return;
+	}
+
+#ifdef POP_AUTH_OPEN_RELAY
+	if (strcasecmp(request->fields.service, "POP3") == 0 ||
+	    strcasecmp(request->fields.service, "IMAP") == 0) {
+		const char *host = net_ip2addr(&request->fields.remote_ip);
+		/* vpopmail 5.4 does not understand IPv6 */
+		if (host[0] != '\0' && IPADDR_IS_V4(&request->fields.remote_ip)) {
+			/* use putenv() directly rather than env_put() which
+			   would leak memory every time we got here. use a
+			   static buffer for putenv() as SUSv2 requirements
+			   would otherwise corrupt our environment later. */
+			static char ip_env[256];
+
+			i_snprintf(ip_env, sizeof(ip_env),
+				   "TCPREMOTEIP=%s", host);
+			putenv(ip_env);
+			open_smtp_relay();
+		}
+	}
+#endif
+
+	callback(PASSDB_RESULT_OK, request);
+}
+
+static struct passdb_module *
+vpopmail_preinit(pool_t pool, const char *args)
+{
+	static bool vauth_load_initialized = FALSE;
+	struct vpopmail_passdb_module *module;
+	const char *const *tmp;
+
+	module = p_new(pool, struct vpopmail_passdb_module, 1);
+	module->module.default_pass_scheme = VPOPMAIL_DEFAULT_PASS_SCHEME;
+	module->module.blocking = TRUE;
+
+	tmp = t_strsplit_spaces(args, " ");
+	for (; *tmp != NULL; tmp++) {
+		if (str_begins(*tmp, "cache_key=")) {
+			module->module.default_cache_key =
+				auth_cache_parse_key(pool, *tmp + 10);
+		} else if (str_begins(*tmp, "webmail=")) {
+			if (net_addr2ip(*tmp + 8, &module->webmail_ip) < 0)
+				i_fatal("vpopmail: Invalid webmail IP address");
+		} else if (strcmp(*tmp, "blocking=no") == 0) {
+			module->module.blocking = FALSE;
+		} else {
+			i_fatal("passdb vpopmail: Unknown setting: %s", *tmp);
+		}
+	}
+	if (!vauth_load_initialized) {
+		vauth_load_initialized = TRUE;
+		if (vauth_open(0) != 0)
+			i_fatal("vpopmail: vauth_open() failed");
+	}
+	return &module->module;
+}
+
+static void vpopmail_deinit(struct passdb_module *module ATTR_UNUSED)
+{
+	vclose();
+}
+
+struct passdb_module_interface passdb_vpopmail = {
+	"vpopmail",
+
+	vpopmail_preinit,
+	NULL,
+	vpopmail_deinit,
+
+	vpopmail_verify_plain,
+	vpopmail_lookup_credentials,
+	NULL
+};
+#else
+struct passdb_module_interface passdb_vpopmail = {
+	.name = "vpopmail"
+};
+#endif
diff -ruN core-2.3.20-original/src/auth/userdb.c core-2.3.20/src/auth/userdb.c
--- core-2.3.20-original/src/auth/userdb.c	2022-12-19 12:38:16.000000000 +0300
+++ core-2.3.20/src/auth/userdb.c	2023-02-09 11:22:36.286856471 +0300
@@ -224,6 +224,7 @@
 extern struct userdb_module_interface userdb_static;
 extern struct userdb_module_interface userdb_passwd;
 extern struct userdb_module_interface userdb_passwd_file;
+extern struct userdb_module_interface userdb_vpopmail;
 extern struct userdb_module_interface userdb_ldap;
 extern struct userdb_module_interface userdb_sql;
 extern struct userdb_module_interface userdb_checkpassword;
@@ -240,6 +241,7 @@
 	userdb_register_module(&userdb_passwd_file);
 	userdb_register_module(&userdb_prefetch);
 	userdb_register_module(&userdb_static);
+	userdb_register_module(&userdb_vpopmail);
 	userdb_register_module(&userdb_ldap);
 	userdb_register_module(&userdb_sql);
 	userdb_register_module(&userdb_checkpassword);
diff -ruN core-2.3.20-original/src/auth/userdb-vpopmail.c core-2.3.20/src/auth/userdb-vpopmail.c
--- core-2.3.20-original/src/auth/userdb-vpopmail.c	1970-01-01 02:00:00.000000000 +0200
+++ core-2.3.20/src/auth/userdb-vpopmail.c	2023-02-09 11:22:36.286856471 +0300
@@ -0,0 +1,202 @@
+/* Copyright (c) 2002-2018 Dovecot authors, see the included COPYING file */
+
+/* Thanks to Courier-IMAP for showing how the vpopmail API should be used */
+
+#include "auth-common.h"
+#include "userdb.h"
+
+#if defined(PASSDB_VPOPMAIL) || defined(USERDB_VPOPMAIL)
+#include "str.h"
+#include "var-expand.h"
+#include "userdb-vpopmail.h"
+
+struct vpopmail_userdb_module {
+	struct userdb_module module;
+
+	const char *quota_template_key;
+	const char *quota_template_value;
+};
+
+struct vqpasswd *vpopmail_lookup_vqp(struct auth_request *request,
+				     char vpop_user[VPOPMAIL_LIMIT],
+				     char vpop_domain[VPOPMAIL_LIMIT])
+{
+	struct vqpasswd *vpw;
+
+	/* vpop_user must be zero-filled or parse_email() leaves an
+	   extra character after the user name. we'll fill vpop_domain
+	   as well just to be sure... */
+	memset(vpop_user, '\0', VPOPMAIL_LIMIT);
+	memset(vpop_domain, '\0', VPOPMAIL_LIMIT);
+
+	if (parse_email(request->fields.user, vpop_user, vpop_domain,
+			VPOPMAIL_LIMIT-1) < 0) {
+		e_info(authdb_event(request),
+		       "parse_email() failed");
+		return NULL;
+	}
+
+	e_debug(authdb_event(request),
+		"lookup user=%s domain=%s",
+		vpop_user, vpop_domain);
+
+	vpw = vauth_getpw(vpop_user, vpop_domain);
+	if (vpw == NULL) {
+		auth_request_log_unknown_user(request, AUTH_SUBSYS_DB);
+		return NULL;
+	}
+
+	return vpw;
+}
+#endif
+
+#ifdef USERDB_VPOPMAIL
+static int
+userdb_vpopmail_get_quota(const char *template, const char *vpop_str,
+			  const char **quota_r, const char **error_r)
+{
+	struct var_expand_table *tab;
+	string_t *quota;
+
+	if (template == NULL || *vpop_str == '\0' ||
+	    strcmp(vpop_str, "NOQUOTA") == 0) {
+		*quota_r = "";
+		return 0;
+	}
+
+	tab = t_new(struct var_expand_table, 2);
+	tab[0].key = 'q';
+	tab[0].value = format_maildirquota(vpop_str);
+
+	quota = t_str_new(128);
+	if (var_expand(quota, template, tab, error_r) < 0)
+		return -1;
+
+	*quota_r = str_c(quota);
+	return 0;
+}
+
+static void vpopmail_lookup(struct auth_request *auth_request,
+			    userdb_callback_t *callback)
+{
+	struct userdb_module *_module = auth_request->userdb->userdb;
+	struct vpopmail_userdb_module *module =
+		(struct vpopmail_userdb_module *)_module;
+	char vpop_user[VPOPMAIL_LIMIT], vpop_domain[VPOPMAIL_LIMIT];
+	struct vqpasswd *vpw;
+	const char *quota, *error;
+	uid_t uid;
+	gid_t gid;
+
+	vpw = vpopmail_lookup_vqp(auth_request, vpop_user, vpop_domain);
+	if (vpw == NULL) {
+		callback(USERDB_RESULT_USER_UNKNOWN, auth_request);
+		return;
+	}
+
+	/* we have to get uid/gid separately, because the gid field in
+	   struct vqpasswd isn't really gid at all but just some flags... */
+	if (vget_assign(vpop_domain, NULL, 0, &uid, &gid) == NULL) {
+		e_info(authdb_event(auth_request),
+		       "vget_assign(%s) failed", vpop_domain);
+		callback(USERDB_RESULT_INTERNAL_FAILURE, auth_request);
+		return;
+	}
+
+	if (auth_request->fields.successful) {
+		/* update the last login only when we're really  */
+		vset_lastauth(vpop_user, vpop_domain,
+			      t_strdup_noconst(auth_request->fields.service));
+	}
+
+	if (vpw->pw_dir == NULL || vpw->pw_dir[0] == '\0') {
+		/* user's homedir doesn't exist yet, create it */
+		e_info(authdb_event(auth_request),
+		       "pw_dir isn't set, creating");
+
+		if (make_user_dir(vpop_user, vpop_domain, uid, gid) == NULL) {
+			e_error(authdb_event(auth_request),
+				"make_user_dir(%s, %s) failed",
+				vpop_user, vpop_domain);
+			callback(USERDB_RESULT_INTERNAL_FAILURE, auth_request);
+			return;
+		}
+
+		/* get the user again so pw_dir is visible */
+		vpw = vauth_getpw(vpop_user, vpop_domain);
+		if (vpw == NULL) {
+			callback(USERDB_RESULT_INTERNAL_FAILURE, auth_request);
+			return;
+		}
+	}
+
+	if (userdb_vpopmail_get_quota(module->quota_template_value,
+				      vpw->pw_shell, &quota, &error) < 0) {
+		e_error(authdb_event(auth_request),
+			"userdb_vpopmail_get_quota(%s, %s) failed: %s",
+			module->quota_template_value,
+			vpw->pw_shell, error);
+		callback(USERDB_RESULT_INTERNAL_FAILURE, auth_request);
+		return;
+	}
+
+	auth_request_set_userdb_field(auth_request, "uid", dec2str(uid));
+	auth_request_set_userdb_field(auth_request, "gid", dec2str(gid));
+	auth_request_set_userdb_field(auth_request, "home", vpw->pw_dir);
+
+	if (*quota != '\0') {
+		auth_request_set_userdb_field(auth_request,
+					      module->quota_template_key,
+					      quota);
+	}
+	callback(USERDB_RESULT_OK, auth_request);
+}
+
+static struct userdb_module *
+vpopmail_preinit(pool_t pool, const char *args)
+{
+	struct vpopmail_userdb_module *module;
+	const char *const *tmp, *p;
+
+	module = p_new(pool, struct vpopmail_userdb_module, 1);
+	module->module.blocking = TRUE;
+
+	for (tmp = t_strsplit(args, " "); *tmp != NULL; tmp++) {
+		if (str_begins(*tmp, "cache_key="))
+			module->module.default_cache_key =
+				p_strdup(pool, *tmp + 10);
+		else if (str_begins(*tmp, "quota_template=")) {
+			p = strchr(*tmp + 15, '=');
+			if (p == NULL) {
+				i_fatal("vpopmail userdb: "
+					"quota_template missing '='");
+			}
+			module->quota_template_key =
+				p_strdup_until(pool, *tmp + 15, p);
+			module->quota_template_value = p_strdup(pool, p + 1);
+		} else if (strcmp(*tmp, "blocking=no") == 0) {
+			module->module.blocking = FALSE;
+		} else
+			i_fatal("userdb vpopmail: Unknown setting: %s", *tmp);
+	}
+	return &module->module;
+}
+
+struct userdb_module_interface userdb_vpopmail = {
+	"vpopmail",
+
+	vpopmail_preinit,
+	NULL,
+	NULL,
+
+	vpopmail_lookup,
+
+	NULL,
+	NULL,
+	NULL
+};
+#else
+struct userdb_module_interface userdb_vpopmail = {
+	.name = "vpopmail"
+};
+#endif
diff -ruN core-2.3.20-original/src/auth/userdb-vpopmail.h core-2.3.20/src/auth/userdb-vpopmail.h
--- core-2.3.20-original/src/auth/userdb-vpopmail.h	1970-01-01 02:00:00.000000000 +0200
+++ core-2.3.20/src/auth/userdb-vpopmail.h	2023-02-09 11:22:36.286856471 +0300
@@ -0,0 +1,17 @@
+#ifndef USERDB_VPOPMAIL_H
+#define USERDB_VPOPMAIL_H
+
+#include <stdio.h>
+#include <vpopmail.h>
+#include <vauth.h>
+
+/* Limit user and domain to 80 chars each (+1 for \0). I wouldn't recommend
+   raising this limit at least much, vpopmail is full of potential buffer
+   overflows. */
+#define VPOPMAIL_LIMIT 81
+
+struct vqpasswd *vpopmail_lookup_vqp(struct auth_request *request,
+				     char vpop_user[VPOPMAIL_LIMIT],
+				     char vpop_domain[VPOPMAIL_LIMIT]);
+
+#endif
diff -ruN core-2.3.20-original/src/master/main.c core-2.3.20/src/master/main.c
--- core-2.3.20-original/src/master/main.c	2022-12-19 12:38:16.000000000 +0300
+++ core-2.3.20/src/master/main.c	2023-02-09 11:22:36.286856471 +0300
@@ -731,6 +731,9 @@
 #ifdef PASSDB_SQL 
 		" sql"
 #endif
+#ifdef PASSDB_VPOPMAIL
+		" vpopmail"
+#endif
 	"\nUserdb:"
 #ifdef USERDB_CHECKPASSWORD
 		" checkpassword"
@@ -759,6 +762,9 @@
 #ifdef USERDB_STATIC 
 		" static"
 #endif
+#ifdef USERDB_VPOPMAIL
+		" vpopmail"
+#endif
 	"\n", IO_BLOCK_SIZE);
 }