If you go to the main page, or any other product page, at the top there is your "Account" link. If you click on that it will show your account information, and under "Notifications" you can set your notifications preferences. You can set your default receiving emails setting to "NO", but then select Multi-Man Publishing from the drop down list and select "YES" to emails from them. This will allow MMP to automatically send you emails about updates to their products that you have purchased, but it will also allow them to send you notifications of sales, new products and such but I actually haven't seen them send out any of those, just updates to their eASLRB title.
You can also set your preferences for receiving Newsletters, Deal of the Day and Follow Your Favorites notices on the same Account page.
If you don't want any notices of any kind you can set everything to "NO" and when you see news of an update here or elsewhere you can just log in to Wargame Vault, click on "My Library" at the top of the page and download an updated version of the title you purchased.
I'm not sure why their last update email didn't get through to you (the last one I see from them was on Feb. 23rd), if you send the email address you use to log-in with to me at stevesmith "at" wargamevault "dot" com I can investigate why you didn't get one and get it fixed.