-# ifdef EXIM_HAVE_OPENSSL_ECDH_AUTO
-/* check if new enough library to support auto ECDH temp key parameter selection */
+/* "auto" needs to be handled carefully.
+ * OpenSSL < 1.0.2: we do not select anything, but fallback to primve256v1
+ * OpenSSL < 1.1.0: we have to call SSL_CTX_set_ecdh_auto
+ * (openss/ssl.h defines SSL_CTRL_SET_ECDH_AUTO)
+ * OpenSSL >= 1.1.0: we do not set anything, the libray does autoselection
+ * https://github.com/openssl/openssl/commit/fe6ef2472db933f01b59cad82aa925736935984b
+ */