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	2008-10-10 11:19:58.000000000 +0100
+++ asterisk-1.4.21.2/apps/app_voicemail.c	2008-10-10 11:20:38.000000000 +0100
@@ -344,6 +344,7 @@
 #ifdef IMAP_STORAGE
 	char imapuser[80];	/* IMAP server login */
 	char imappassword[80];	/* IMAP server password if authpassword not defined */
+        char imapmbxid[80];     /* Shared mailbox ID to use rather than the dial in one */
 #endif
 	double volgain;		/*!< Volume gain for voicemails sent via email */
 	AST_LIST_ENTRY(ast_vm_user) list;
@@ -603,6 +604,8 @@
 		ast_copy_string(vmu->imapuser, value, sizeof(vmu->imapuser));
 	} else if (!strcasecmp(var, "imappassword")) {
 		ast_copy_string(vmu->imappassword, value, sizeof(vmu->imappassword));
+	} else if (!strcasecmp(var, "imapmbxid")) {
+	        ast_copy_string(vmu->imapmbxid, value, sizeof(vmu->imapmbxid));
 #endif
 	} else if (!strcasecmp(var, "delete") || !strcasecmp(var, "deletevoicemail")) {
 		ast_set2_flag(vmu, ast_true(value), VM_DELETE);	
@@ -707,6 +710,8 @@
 			ast_copy_string(retval->imapuser, tmp->value, sizeof(retval->imapuser));
 		} else if (!strcasecmp(tmp->name, "imappassword")) {
 			ast_copy_string(retval->imappassword, tmp->value, sizeof(retval->imappassword));
+		} else if (!strcasecmp(tmp->name, "imapmbxid")) {
+		        ast_copy_string(retval->imapmbxid, tmp->value, sizeof(retval->imapmbxid));
 #endif
 		} else
 			apply_option(retval, tmp->name, tmp->value);
@@ -1866,7 +1871,11 @@
 		/* fprintf(p, "X-Asterisk-VM-Orig-Mailbox: %s" ENDL, ext); */
 		fprintf(p, "X-Asterisk-VM-Server-Name: %s" ENDL, fromstring);
 		fprintf(p, "X-Asterisk-VM-Context: %s" ENDL, context);
+#ifdef IMAP_STORAGE
+		fprintf(p, "X-Asterisk-VM-Extension: %s" ENDL, ((vmu->imapmbxid[0] != '\0')?vmu->imapmbxid:mailbox));
+#else
 		fprintf(p, "X-Asterisk-VM-Extension: %s" ENDL, mailbox);
+#endif
 		fprintf(p, "X-Asterisk-VM-Priority: %d" ENDL, chan->priority);
 		fprintf(p, "X-Asterisk-VM-Caller-channel: %s" ENDL, chan->name);
 		fprintf(p, "X-Asterisk-VM-Caller-ID-Num: %s" ENDL, cidnum);
@@ -2493,7 +2502,7 @@
 	if (ret == 0) {
 	        ast_mutex_lock(&vms_p->lock);
 		pgm = mail_newsearchpgm ();
-		hdr = mail_newsearchheader ("X-Asterisk-VM-Extension", (char *)mailbox);
+		hdr = mail_newsearchheader ("X-Asterisk-VM-Extension", (char *)((vmu->imapmbxid[0] != '\0')?vmu->imapmbxid:mailbox));
 		pgm->header = hdr;
 		if (fold != 1) {
 			pgm->unseen = 1;
@@ -4857,7 +4866,7 @@
 	pgm = mail_newsearchpgm();
 
 	/* Check IMAP folder for Asterisk messages only... */
-	hdr = mail_newsearchheader ("X-Asterisk-VM-Extension", vmu->mailbox);
+	hdr = mail_newsearchheader ("X-Asterisk-VM-Extension", ((vmu->imapmbxid[0] != '\0')?vmu->imapmbxid:vmu->mailbox));
 	pgm->header = hdr;
 	pgm->deleted = 0;
 	pgm->undeleted = 1;