--- dovecot-2.1.6/src/lib-storage/mail-storage.c.orig	2012-05-23 11:45:55.000000000 +0100
+++ dovecot-2.1.6/src/lib-storage/mail-storage.c	2012-05-23 12:11:28.000000000 +0100
@@ -22,12 +22,13 @@
 #include "mailbox-guid-cache.h"
 
 #include <stdlib.h>
 #include <ctype.h>
 
 #define MAILBOX_DELETE_RETRY_SECS (60*5)
+#define MAX_MSGS_PER_MAILBOX 4000
 
 extern struct mail_search_register *mail_search_register_imap;
 extern struct mail_search_register *mail_search_register_human;
 
 struct mail_storage_module_register mail_storage_module_register = { 0 };
 struct mail_module_register mail_module_register = { 0 };
@@ -1620,22 +1621,28 @@
 	ctx->dest_mail = mail;
 }
 
 int mailbox_save_begin(struct mail_save_context **ctx, struct istream *input)
 {
 	struct mailbox *box = (*ctx)->transaction->box;
+	struct mailbox_status status;
 	int ret;
 
 	if (mail_index_is_deleted(box->index)) {
 		mailbox_set_deleted(box);
 		return -1;
 	}
 
 	if (!(*ctx)->copying_via_save)
 		(*ctx)->saving = TRUE;
-	if (box->v.save_begin == NULL) {
+	mailbox_get_status(box, STATUS_MESSAGES, &status);
+	if (status.messages >= MAX_MSGS_PER_MAILBOX) {
+		mail_storage_set_error(box->storage, MAIL_ERROR_NOSPACE,
+					"Mailbox full: Too many messages");
+		ret = -1;
+	} else if (box->v.save_begin == NULL) {
 		mail_storage_set_error(box->storage, MAIL_ERROR_NOTPOSSIBLE,
 				       "Saving messages not supported");
 		ret = -1;
 	} else {
 		ret = box->v.save_begin(*ctx, input);
 	}
@@ -1685,23 +1692,31 @@
 
 int mailbox_copy(struct mail_save_context **_ctx, struct mail *mail)
 {
 	struct mail_save_context *ctx = *_ctx;
 	struct mailbox *box = ctx->transaction->box;
 	struct mail_keywords *keywords = ctx->keywords;
+	struct mailbox_status status;
 	int ret;
 
 	*_ctx = NULL;
 
 	if (mail_index_is_deleted(box->index)) {
 		mailbox_set_deleted(box);
 		mailbox_save_cancel(&ctx);
 		return -1;
 	}
 
-	ret = ctx->transaction->box->v.copy(ctx, mail);
+	mailbox_get_status(box, STATUS_MESSAGES, &status);
+	if (status.messages >= MAX_MSGS_PER_MAILBOX) {
+		mail_storage_set_error(box->storage, MAIL_ERROR_NOSPACE,
+					"Mailbox full: Too many messages");
+		ret = -1;
+	} else {
+		ret = ctx->transaction->box->v.copy(ctx, mail);
+	}
 	if (keywords != NULL)
 		mailbox_keywords_unref(&keywords);
 	return ret;
 }
 
 int mailbox_save_using_mail(struct mail_save_context **ctx, struct mail *mail)