Be straightforward about your intent and ask users to share email for feedback or whatever reason and if they want let them disclose voluntarily. Whatever goods or services you provide, do so in exchange for money only, absolutley anything else that is mandatory is a cost to users. This is not just an online thing, I get ever so more infuriated when they hassle me about giving them info at a brick and mortar store.
I worked for my money, the only reason I am not just taking your stuff or forcing you to provide me service is because we have laws where all are equal and I am not your subject that you get to offer or deny me goods and services in exchange for compelling me to do things. I exchange my time and labor for wages so that I can exchange these taxed (!!) wages in exchange for goods and services. This attempt to subvert the social contract which is the foundation of government, liberty and commerce is as old as civilized society. There were many times in the past (recent ones being jim crow era, apartheid, nazi germany to name a few) where ability to engage in commerce was dictated by businesses against individuals as a means of subjugating others. Abuse of the priviledge to engage in commerce in order to implement some other agenda.
I don't care if you just want to tell people about new product updates or you have a more malicious intent, my money is legal tendor and if commerical entities have power to deny business based on my identity then I no longer have equal voice or power as everyone else, I no longer enjoy the same privilege of being able to exchange wages for goods and services because of my identity.
I mean this is absolutley enraging to me. I was initially hesitant but I listened to reason and decided to get vaccinated, guess what? The amount of questions they ask is intolerable, all sort of crap that had nothing to do with being vaccinated. Home address, employer, phone number, email address. And they didn't even care about the vaccination card enough to fill out my name on it, they gave me a blank card to put any name I want on it. at least they collected my info.
This imbalance of power between individuals and businesses is unsustainable. If someone can compel you to disclose information, they are excercising power over you. if you are unable to do the same to them, there is inequality, an imbalance of power. Neither the government nor businesses should be able to collect information about people beyond what is demonstrably and transparently neccesary to provide goods and services in exchange for taxed or paid wages. This is as much a failure of government as it is inability of society to catch up with the imbalances of power and perverse incentives created by modern technology (but like I said, even without technology information about people's identity was abused against them this way, except tech empowers malice as much as it does benevolence)
Sorry for the rant, just a pet-peeve of mine.