You really need to activate URL rewriting on
www.machsupport.com so that all old links to forum posts are redirected to the right forum post at forum.macsupport.com.
Shouldn't be hard since all that is needed is to replace
www.machsupport.com/forum/* with forum.machsupport.com/forum/*
Now all internal links, external links plus Google and other search links to forum posts are dead.
You also need to fix the forum search function. It now fails with an error:
2: pspell_new(): PSPELL couldn't open the dictionary. reason: No word lists can be found for the language "en".
File: /var/www/vhosts/machsupport.com/forum.machsupport.com/forum/Sources/Search.php
Line: 700