343 Industries has started sending out access code for all Halo 4 specializations via email to people who logged into the game as late as November 20. ”Codes giving early access to six Specializations were sent yesterday. I’m currently following up with that team to find out if all the emails have been sent (UPDATE: All emails have been sent),” 343 Indistrues community manager Jessica Shea wrote on Halo Waypoint. If you did play it, but didn’t receive an email entitled “You have a gift from Xbox LIVE,” then something is preventing you from doing so. If you didn’t actually play it, but think you did, that might be one of the reasons. Another one includes being a resident of Europe, the Middle East or Africa, and thinking those regions were eligible for the specializations post-launch, when they weren’t. They were offered as pre-order bonuses.
Another thing you’re advised to do is check your spam folder for the email. Also note that while all of them might be available to you already, Specializations aren’t actually usable until you reach level 50. If you’re absolutely certain that you should be getting this email, but aren’t, you should send a message via Twitter to @XboxSupport or contact them via their website. Another thing that might have happened is that since “the codes were sent to the email address that you used when you signed up for your Gamertag. If you are now using a different email address but did not change it with Xbox LIVE, the code will have been sent to the email address associated with your Gamertag as of November 20.” Meaning you should check your previous email.
Article from Gamersyndrome.com