diff -ruN asterisk-1.4.21.2-save/apps/app_voicemail.c asterisk-1.4.21.2/apps/app_voicemail.c
--- asterisk-1.4.21.2-save/apps/app_voicemail.c	2008-05-27 18:17:20.000000000 +0100
+++ asterisk-1.4.21.2/apps/app_voicemail.c	2008-10-10 11:03:04.000000000 +0100
@@ -908,7 +908,9 @@
 		ast_log(LOG_DEBUG, "deleting msgnum %d, which is mailbox message %lu\n",msgnum,messageNum);
 	/* delete message */
 	snprintf (arg, sizeof(arg), "%lu",messageNum);
+	ast_mutex_lock(&vms->lock);
 	mail_setflag (vms->mailstream,arg,"\\DELETED");
+	ast_mutex_unlock(&vms->lock);
 }
 
 #endif
@@ -2401,8 +2403,10 @@
 		INIT(&str, mail_string, buf, len);
 		init_mailstream(vms, 0);
 		imap_mailbox_name(mailbox, sizeof(mailbox), vms, 0, 1);
+		ast_mutex_lock(&vms->lock);
 		if (!mail_append(vms->mailstream, mailbox, &str))
 			ast_log(LOG_ERROR, "Error while sending the message to %s\n", mailbox);
+		ast_mutex_unlock(&vms->lock);
 		fclose(p);
 		unlink(tmp);
 		ast_free(buf);
@@ -2487,6 +2491,7 @@
 		return -1;
 	}
 	if (ret == 0) {
+	        ast_mutex_lock(&vms_p->lock);
 		pgm = mail_newsearchpgm ();
 		hdr = mail_newsearchheader ("X-Asterisk-VM-Extension", (char *)mailbox);
 		pgm->header = hdr;
@@ -2512,10 +2517,13 @@
 			vms_p->oldmessages = vms_p->vmArrayIndex;
 		/*Freeing the searchpgm also frees the searchhdr*/
 		mail_free_searchpgm(&pgm);
+		ast_mutex_unlock(&vms_p->lock);
 		vms_p->updated = 0;
 		return vms_p->vmArrayIndex;
-	} else {  
+	} else {
+	        ast_mutex_lock(&vms_p->lock);
 		mail_ping(vms_p->mailstream);
+		ast_mutex_unlock(&vms_p->lock);
 	}
 	return 0;
 }
@@ -2614,8 +2622,12 @@
 		return -1;
 	}
 	snprintf(messagestring, sizeof(messagestring), "%ld", sendvms->msgArray[msgnum]);
-	if ((mail_copy(sendvms->mailstream, messagestring, (char *) mbox(imbox)) == T))
+	ast_mutex_lock(&sendvms->lock);
+	if ((mail_copy(sendvms->mailstream, messagestring, (char *) mbox(imbox)) == T)) {
+	        ast_mutex_unlock(&sendvms->lock);
 		return 0;
+	}
+	ast_mutex_unlock(&sendvms->lock);
 	ast_log(LOG_WARNING, "Unable to copy message from mailbox %s to mailbox %s\n", vmu->mailbox, recip->mailbox);
 	return -1;
 }
@@ -3260,7 +3272,9 @@
 	snprintf(sequence, sizeof(sequence), "%ld", vms->msgArray[msg]);
 	if (option_debug > 2)
 		ast_log(LOG_DEBUG, "Copying sequence %s to mailbox %s\n",sequence,(char *) mbox(box));
-	res = mail_copy(vms->mailstream,sequence,(char *) mbox(box));
+	ast_mutex_lock(&vms->lock);
+	res = mail_copy(vms->mailstream,sequence,(char *) mbox(box));	
+	ast_mutex_unlock(&vms->lock);
 	if (res == 1) return 0;
 	return 1;
 #else
@@ -4174,7 +4188,9 @@
 				}
 
 				/* This will only work for new messages... */
+				ast_mutex_lock(&vms->lock);
 				header_content = mail_fetchheader (vms->mailstream, vms->msgArray[vms->curmsg]);
+				ast_mutex_unlock(&vms->lock);
 				/* empty string means no valid header */
 				if (ast_strlen_zero(header_content)) {
 					ast_log (LOG_ERROR,"Could not fetch header for message number %ld\n",vms->msgArray[vms->curmsg]);
@@ -4207,7 +4223,9 @@
 				if (option_debug > 2)
 					ast_log (LOG_DEBUG,"Before mail_fetchstructure, message number is %ld, filename is:%s\n",vms->msgArray[vms->curmsg], vms->fn);
 				/*mail_fetchstructure (mailstream, vmArray[0], &body); */
+				ast_mutex_lock(&vms->lock);
 				mail_fetchstructure (vms->mailstream, vms->msgArray[vms->curmsg], &body);
+				ast_mutex_unlock(&vms->lock);
 				save_body(body,vms,"3","gsm");
 				/* should not assume "fmt" here! */
 				save_body(body,vms,"2",fmt);
@@ -4506,7 +4524,9 @@
 	}
 
 	/* This will only work for new messages... */
+	ast_mutex_lock(&vms->lock);
 	header_content = mail_fetchheader (vms->mailstream, vms->msgArray[vms->curmsg]);
+	ast_mutex_unlock(&vms->lock);
 	/* empty string means no valid header */
 	if (ast_strlen_zero(header_content)) {
 		ast_log (LOG_ERROR,"Could not fetch header for message number %ld\n",vms->msgArray[vms->curmsg]);
@@ -4515,8 +4535,9 @@
 	snprintf(todir, sizeof(todir), "%s%s/%s/tmp", VM_SPOOL_DIR, vmu->context, vmu->mailbox);
 	make_gsm_file(vms->fn, sizeof(vms->fn), vms->imapuser, todir, vms->curmsg);
 
+	ast_mutex_lock(&vms->lock);
 	mail_fetchstructure (vms->mailstream,vms->msgArray[vms->curmsg],&body);
-	
+	ast_mutex_lock(&vms->lock);
 	/* We have the body, now we extract the file name of the first attachment. */
 	if (body->nested.part && body->nested.part->next && body->nested.part->next->body.parameter->value) {
 		attachedfilefmt = ast_strdupa(body->nested.part->next->body.parameter->value);
@@ -4832,6 +4853,7 @@
 		check_quota(vms,(char *)mbox(box));
 	}
 
+	ast_mutex_lock(&vms->lock);
 	pgm = mail_newsearchpgm();
 
 	/* Check IMAP folder for Asterisk messages only... */
@@ -4858,6 +4880,7 @@
 	vms->lastmsg = vms->vmArrayIndex - 1;
 
 	mail_free_searchpgm(&pgm);
+	ast_mutex_unlock(&vms->lock);
 	return 0;
 }
 #else
@@ -6989,12 +7012,14 @@
 	if (option_debug > 2)
 		ast_log(LOG_DEBUG, "*** Checking if we can expunge, deleted set to %d, expungeonhangup set to %d\n",deleted,expungeonhangup);
 	if (vmu && deleted == 1 && expungeonhangup == 1) {
+	        ast_mutex_lock(&vms.lock);
 #ifdef HAVE_IMAP_TK2006
 		if (LEVELUIDPLUS (vms.mailstream)) {
 			mail_expunge_full(vms.mailstream,NIL,EX_UID);
 		} else 
 #endif
 			mail_expunge(vms.mailstream);
+		ast_mutex_unlock(&vms.lock);
 	}
 	/*  before we delete the state, we should copy pertinent info
 	 *  back to the persistent model */
@@ -8052,7 +8077,9 @@
 	}
 
 	/* This will only work for new messages... */
+	ast_mutex_lock(&vms->lock);
 	header_content = mail_fetchheader (vms->mailstream, vms->msgArray[vms->curmsg]);
+	ast_mutex_unlock(&vms->lock);
 	/* empty string means no valid header */
 	if (ast_strlen_zero(header_content)) {
 		ast_log (LOG_ERROR,"Could not fetch header for message number %ld\n",vms->msgArray[vms->curmsg]);
@@ -9102,7 +9129,9 @@
 	
 	if (!body || body == NIL)
 		return -1;
+	ast_mutex_lock(&vms->lock);
 	body_content = mail_fetchbody (vms->mailstream, vms->msgArray[vms->curmsg], section, &len);
+	ast_mutex_unlock(&vms->lock);
 	if (body_content != NIL) {
 		snprintf(filename, sizeof(filename), "%s.%s", vms->fn, format);
 		/* ast_log (LOG_DEBUG,body_content); */
@@ -9113,6 +9142,7 @@
 }
 
 /* get delimiter via mm_list callback */
+/* MUTEX should already be held */
 static void get_mailbox_delimiter(MAILSTREAM *stream) {
 	char tmp[50];
 	snprintf(tmp, sizeof(tmp), "{%s}", imapserver);
@@ -9121,6 +9151,7 @@
 
 /* Check Quota for user */
 static void check_quota(struct vm_state *vms, char *mailbox) {
+        ast_mutex_lock(&vms->lock);
 	mail_parameters(NULL, SET_QUOTA, (void *) mm_parsequota);
 	if (option_debug > 2)
 		ast_log(LOG_DEBUG, "Mailbox name set to: %s, about to check quotas\n", mailbox);
@@ -9129,6 +9160,7 @@
 	} else {
 		ast_log(LOG_WARNING,"Mailstream not available for mailbox: %s\n",mailbox);
 	}
+	ast_mutex_unlock(&vms->lock);
 }
 
 #endif /* IMAP_STORAGE */