I entered one of those opt-in giveaways a couple of weeks ago. You've probably seen them, it's a co-marketed by a few companies with a "win all these prizes" for opting in, social sharing, etc.
I knew and trusted about half the companies so I wasn't worried about the spam risk.
The funny thing was that with two exceptions, none of the companies did a really good job with their email content.
Three of them haven't emailed me at all.
Two just put me on their normal promotion list with is full of image emails with no content.
Two of them (ones I trust) are sending half decent emails but nothing about the giveaway. Passable but still very weak.
These companies could have easily setup an email sequence to send to subscribers with specific giveaway-based content. Things like "giveaway ends in 1 week" or "special discount code for 10% off for giveaway subscribers only" or even a joint promotion "buy X from Acme Company and get Y from Big Corp".
Basically a special form of a New Customer Welcome campaign but for potential customers who came during a special promotion.
Instead it's just generic emails.
Emails I've already archiving unread and considering unsubscribing from.
It could have been so much better.
But that's how I feel about most email campaigns these days.
They could have been better.
At the very least I hope the companies track the performance of the giveaway subscribers.
Using a cohort analysis like in my app would let them compare the performance of customers acquired this month (giveaway month) against customers acquired in other months. If the giveaway month outperforms the other cohorts, that's a sign that the giveaway worked even with poor email content.
An even better option would be to have that special campaign for the giveaway itself and track purchases made from there (e.g. UTM links).