I don't verify addresses, but I do include unsubscribe instructions. Is that enough?
You must always verify addresses added to your mailing list. It’s never acceptable to add recipients to your mailing list on the assumption that they’ll unsubscribe if they were added without giving permission.
If people are subscribed to your list against their will, either by accident or by another malicious person, they won’t consider the mail to be legitimate. They won’t know whether you’re a spammer or not, and probably won’t use the unsubscribe instructions you provide: people have been told by reputable sources such as Consumer Reports magazine that they should never try to follow the “removal” instructions in an unsolicited message that they didn’t sign up for.
So the recipients will likely ignore the first few messages you send, then report you as a “persistent spammer” if the messages keep coming — and they’ll be right, in the sense that they didn’t ask to get anything from you but you keep sending unsolicited mail.
Compare this to what happens when you use a proper verification system. If you verify the address and the recipient ignores it, the recipient will receive only one message from you and probably won’t complain. Even if people do complain, it will be a one-time problem, not an ongoing problem — and no anti-spam organization or ISP treats reasonable subscription verification messages as “spam”.