1 files changed, 4 insertions, 0 deletions
diff --git a/lib/imap.c b/lib/imap.c
index 923b1d59b..6163899bb 100644
--- a/lib/imap.c
+++ b/lib/imap.c
@@ -963,6 +963,10 @@ static CURLcode imap_state_starttls_resp(struct Curl_easy *data,
 
   (void)instate; /* no use for this yet */
 
+  /* Pipelining in response is forbidden. */
+  if(data->conn->proto.imapc.pp.cache_size)
+    return CURLE_WEIRD_SERVER_REPLY;
+
   if(imapcode != IMAP_RESP_OK) {
     if(data->set.use_ssl != CURLUSESSL_TRY) {
       failf(data, "STARTTLS denied");