+/* iconv arg2 type: libiconv in Ports uses "const char* * inbuf" and was
+ * traditionally the only approach available. The iconv functionality
+ * in libc is "char ** restrict src".
+ *
+ * <https://www.freebsd.org/doc/en/books/porters-handbook/using-iconv.html>
+ * says that libc has iconv since 2013, in 10-CURRENT. FreeBSD man-pages
+ * shows it included in 10.0-RELEASE. Writing this in 2017, 10.3 is the
+ * oldest supported release, so we should assume non-libiconv by default.
+ * (Actually, people still using old releases past EOL; we shouldn't support
+ * them but I don't want to deal with howls of complaints because we dare
+ * to not support the unsupported, so guard this on FreeBSD 10+)
+ *
+ * Thus we no longer override iconv.
+ *
+ * However, if libiconv is installed, and anything adds /usr/local/include
+ * to include-path (likely) then we'll get that. So define a variable
+ * which makes the libiconv try to not interfere with OS iconv.
+ */
+#if __FreeBSD__ >= 10
+# define LIBICONV_PLUG
+#endif
+/* for more specific version constraints, include <sys/param.h> and look at
+ * __FreeBSD_version */
+
+
+/* When using DKIM, setting OS_SENDFILE can increase
+performance on outgoing mail a bit. */
+
+#define OS_SENDFILE
+extern ssize_t os_sendfile(int, int, off_t *, size_t);