Mail: handling of LOGIN IMAP command untagged response.

In particular, an untagged CAPABILITY response as described in the
interim RFC 3501 internet drafts was seen in various IMAP servers.
Previously resulted in a broken connection, now an untagged response
is proxied to client.

src/mail/ngx_mail_proxy_module.c

@@ -1019,12 +1019,36 @@ ngx_mail_proxy_read_response(ngx_mail_session_t *s, ngx_uint_t state)
             break;
 
         case ngx_imap_passwd:
+
+            /*
+             * untagged CAPABILITY response (draft-crispin-imapv-16),
+             * known to be sent by SmarterMail and Gmail
+             */
+
+            if (p[0] == '*' && p[1] == ' ') {
+                p += 2;
+
+                while (p < b->last - 1) {
+                    if (p[0] == CR && p[1] == LF) {
+                        p += 2;
+                        break;
+                    }
+
+                    p++;
+                }
+
+                if (b->last - p < 4) {
+                    return NGX_AGAIN;
+                }
+            }
+
             if (ngx_strncmp(p, s->tag.data, s->tag.len) == 0) {
                 p += s->tag.len;
                 if (p[0] == 'O' && p[1] == 'K') {
                     return NGX_OK;
                 }
             }
+
             break;
         }