diff -Naur cyrus-imapd-2.1.16/imap/lmtpd.c cyrus-imapd-2.1.16.autosievefolder/imap/lmtpd.c
--- cyrus-imapd-2.1.16/imap/lmtpd.c	2003-10-01 21:20:37.000000000 +0300
+++ cyrus-imapd-2.1.16.autosievefolder/imap/lmtpd.c	2003-11-27 16:40:19.669212000 +0200
@@ -148,6 +148,9 @@
 struct lmtp_func mylmtp = { &deliver, &verify_user, &shut_down,
 			    &spoolfile, &removespool, 0, 1, 0 };
 
+static int autosieve_subfolder(char *userid, struct auth_state *auth_state,
+			       char *subfolder);
+
 static void logdupelem();
 static void usage();
 static void setup_sieve();
@@ -692,6 +695,19 @@
                           sd->username, mdata->notifyheader,
                           fc->mailbox, quotaoverride, 0);
 
+    if (ret == IMAP_MAILBOX_NONEXISTENT) {
+    /* if "plus" folder under INBOX, then try to create it */
+        ret = autosieve_subfolder(sd->username, sd->authstate, fc->mailbox);
+
+        if (!ret)
+           ret = deliver_mailbox(md->data, mdata->stage, md->size,
+                          fc->imapflags->flag, fc->imapflags->nflags,
+                          sd->username, sd->authstate, md->id,
+                          sd->username, mdata->notifyheader,
+                          fc->mailbox, quotaoverride, 0);
+
+    }
+
     if (ret == 0) {
 
 	snmp_increment(SIEVE_FILEINTO, 1);
@@ -1498,3 +1514,86 @@
 
     append_removestage(stage);
 }
+
+
+#define SEP '|'
+
+static int autosieve_subfolder(char *userid, struct auth_state *auth_state,
+                              char *subfolder) {
+    char foldername [MAX_MAILBOX_NAME+1];
+    char f [MAX_MAILBOX_NAME+1];
+    const char *subf ;
+    char *p, *q, *next_subf, *mbox;
+    int len, r;
+    int createsievefolder = 0;
+
+  
+   /* Check if subfolder is NULL */ 
+   if(subfolder == NULL) 
+      return IMAP_MAILBOX_NONEXISTENT; 
+
+   if ((subfolder[0] != 'i' && subfolder[0] != 'I') ||
+                 strncasecmp(subfolder, "inbox", 5) ||
+              subfolder[5] != lmtpd_namespace.hier_sep)
+       return IMAP_MAILBOX_NONEXISTENT;
+
+
+   if (config_getswitch("anysievefolder", NULL))
+       createsievefolder = 1;
+   else if ((subf = config_getstring("autosievefolders", NULL)) != NULL) {
+            /*
+             * mbox contains only the subfolder to be created name
+             */
+             mbox = strchr(subfolder, (int) lmtpd_namespace.hier_sep); 
+             mbox++;
+
+             /* Roll through subf */
+             next_subf = (char *) subf;
+             while (*next_subf) {
+                   for (p = next_subf ; isspace((int) *p) || *p == SEP ; p++);
+                   for (next_subf = p ; *next_subf && *next_subf != SEP ; next_subf++);
+                   for (q = next_subf ; q > p && (isspace((int) *q) || *q == SEP || !*q); q--);
+      
+                   if (!*p) continue;
+                   /*
+                    * This is a preliminary length check based on the assumption
+                    * that the *final* internal format will be something
+                    * like user.userid.subfolder(s).
+                    */
+                   if (len  > sizeof(f) - strlen(userid) - 5)
+                       r = IMAP_MAILBOX_BADNAME;
+
+                   if (!r) {
+                       strncpy(f, p, len);
+                       f[len] = '\0';
+                   }
+
+                   if (!strcmp(f, mbox)) {
+                       createsievefolder = 1;
+		       break;
+                   }
+             }              
+        }
+
+   if (createsievefolder) {
+       /* Translate any separators in user */
+       if (userid) mboxname_hiersep_tointernal(&lmtpd_namespace, userid);
+   
+       r = (*lmtpd_namespace.mboxname_tointernal) (&lmtpd_namespace,
+                                              subfolder, userid, foldername);
+       if (!r)
+           r = mboxlist_createmailbox(foldername, MAILBOX_FORMAT_NORMAL, NULL,
+                                          1, userid, auth_state, 0, 0, 0);
+       if (!r) {
+           mboxlist_changesub(foldername, userid, auth_state, 1, 1);
+           syslog(LOG_DEBUG, "Ondemand subfolder: User %s, subfolder %s creation succeeded.",
+                                                  userid, foldername);
+           return 0;
+       } else {
+           syslog(LOG_ERR, "Requested subfolder: User %s, subfolder %s creation failed. %s",
+                                                 userid, foldername,error_message(r));
+           return r;
+       }
+   } else 
+       return IMAP_MAILBOX_NONEXISTENT;
+}