+/* If there's no EHLO/HELO data, we can't show it. */
+
+if (sender_helo_name == NULL) show_helo = FALSE;
+
+/* If HELO/EHLO was followed by an IP literal, it's messy because of two
+features of IPv6. Firstly, there's the "IPv6:" prefix (Exim is liberal and
+doesn't require this, for historical reasons). Secondly, IPv6 addresses may not
+be given in canonical form, so we have to canonicize them before comparing. As
+it happens, the code works for both IPv4 and IPv6. */
+
+else if (sender_helo_name[0] == '[' &&
+ sender_helo_name[(len=Ustrlen(sender_helo_name))-1] == ']')
+ {
+ int offset = 1;
+ uschar *helo_ip;
+
+ if (strncmpic(sender_helo_name + 1, US"IPv6:", 5) == 0) offset += 5;
+ if (strncmpic(sender_helo_name + 1, US"IPv4:", 5) == 0) offset += 5;
+
+ helo_ip = string_copyn(sender_helo_name + offset, len - offset - 1);
+
+ if (string_is_ip_address(helo_ip, NULL) != 0)
+ {
+ int x[4], y[4];
+ int sizex, sizey;
+ uschar ipx[48], ipy[48]; /* large enough for full IPv6 */
+
+ sizex = host_aton(helo_ip, x);
+ sizey = host_aton(sender_host_address, y);
+
+ (void)host_nmtoa(sizex, x, -1, ipx, ':');
+ (void)host_nmtoa(sizey, y, -1, ipy, ':');
+
+ if (strcmpic(ipx, ipy) == 0) show_helo = FALSE;
+ }
+ }
+