Subscription to a mailing list is not advertised to nor consented by the customer. Not when buying a game, nor when buying a bundle.
And there is no way to either give consent or revoke consent before getting such a mail.
I see mulitple problems here. This feature needs a major rework.
For your needs, there needs to be a way to resubscribe to the mailing list - without having such a mail.
As for your assumption that people give consent by buying a cheap bundle, and that developers would join bundles to be able to send mails, I have serious doubts.
This mail feature is not bundle specific. It is active for all purchases. It only gets visible on big bundles, because some developers are bound to send some mails. Prompting overly negative reactions from most users, usage of spam filters, deactivation of mail options alltogether and complain threads in community. People know they did not consent to a mailing list and are alienated by receiving mails this way.
That mailing list thingy needs an opt-in button on the purchase page. Not an automatic subscription with an opt-out.


