+/* It's not .so for dynamic libraries on Darwin. */
+#define DYNLIB_FN_EXT "dylib"
+
+/* We currently need some assistance getting OFF_T_FMT correct on MacOS */
+#ifdef OFF_T_FMT
+# undef OFF_T_FMT
+#endif
+#define OFF_T_FMT "%lld"
+#define LONGLONG_T long int
+
+/* default is non-const */
+#define ICONV_ARG2_TYPE const char **
+
+/* seems arpa/nameser.h does not define this */
+#define NS_MAXMSG 65535
+
+/* There may be very many supplementary groups for the user. See notes
+in "man 2 getgroups". */
+#define _DARWIN_UNLIMITED_GETGROUPS
+#define EXIM_GROUPLIST_SIZE 64
+
+/* TCP Fast Open: Darwin uses a connectx() call
+rather than a modified sendto() */
+#define EXIM_TFO_CONNECTX
+