No one likes to open their email to hundreds of ads in their inbox waiting to be opened. Most people will just mark all as read or send them right to the trash. I personally, made a separate email account to use at stores so I do not have one inbox overflowing with emails that I will not read or engage with.
Companies are now adding an unsubscribe button at the bottom of their emails to give customers an easy way to opt-out of ads. Another way that companies can make sure they their customers want to receive emails is by having a double opt-in, instead of just one. Single opt-in usually results in lots of fake emails, leaving the company with hard bounced emails.
Customers would be more receptive to a weekly email outlining the deals of the week, rather than multiple emails a day about deals for today and tomorrow, just to see them again the next day. Nudge marketing works best when there is a deal included. If you receive an email saying “you left something in your cart” and there is a $10 off coupon in the email, a customer is more likely to go back and buy the item(s) in the cart because they are reminded and offered a deal.