I don't think that's a valid assumption. The confirmation email you get is a standard one-off email; the other is a distribution list which can have different spam rules. Bulk email probably starts with a high "spamminess" coefficient so it might not take much for your ISP to block it.
Since your name would automatically be added to the list the problem lies somewhere after that point. Either the sending program doesn't like your email address or your ISP doesn't like the daily notification.
Also, spam filters block known spammers by domain names. Only emails from those you specify as an "approved sender" will automatically bypass the spam filters. You could make "giveawayoftheday.com" an "approved sender" and see what happens.