1. Marketers should make it clear and easy for people to unsubscribe. The only truly acceptable method for unsubscribing is to offer a link to a Web page with this text: "Click Here to Unsubscribe." Anything else puts too much onus on the recipient and will likely compel the recipient to hit the "report spam" button in his or her email client. Also, recipients should not need to log in, recall an account number, or type in a password in order to unsubscribe. One best practice to reduce recipient pain is to include the email address in the unsubscribe link, allowing the unsubscribe form to automatically accept the request with one click. Another alternative is to offer just one form item on the unsubscribe page, and allow users to enter their email address and click a button to unsubscribe. I understand per your fellow columnist Loren McDonald's recent best practice story, some recipients are simply trying to change their preferences. It's a good point, so put that link on the unsubscribe page. This response is tailored around the folks that truly wish to end communications with the sender.
2. Process the unsubscribe request instantly. CAN-SPAM may allow marketers to fulfill unsubscribe requests within 10 days, but users expect it to happen faster, aren't likely to know about the 10-day rule and, quite frankly, don't care -- why should they? So, wait if you must but understand that you do so at the expense of your fine brand and will likely upset quite a few members that might just return if you treat them well. Our experience is that consumers who continue to receive mail after they've unsubscribed, even if that unsubscribe was yesterday or the day before, just don't accept that. If you send mail to someone who doesn't want it, they'll rightfully perceive you as a spammer. This may compel them to simply hit the "report spam" button -- which could affect your deliverability in the future or worse, lead to escalated action.
3. Offer options. Some companies only offer an email-based unsubscribe options (for example, "Reply to this message with 'Unsubscribe' in the subject line") and some only offer Web-based unsubscribes (example: "click here to unsubscribe"). The best marketers offers users both methods, and they test each method to make sure they work reliably. Users that are on mobile devices may only be able to reply to your email. Users that have email forwarded from another account may only be able to click a link to a Web page. Marketers should allow both options all the time.
5. Respect the unsubscribe request. CAN-SPAM requires you to opt out users from all commercial email when they request it. So, if firstname.lastname@example.org unsubscribes from your newsletter, there's a good chance that he doesn't want to receive an unsolicited email from your sales reps, or another department. The law requires you to honor that request. A best practice would be to offer multiple options on the opt-out page (like MediaPost does on its account management page), so you can make sure you're respecting your users' wishes. If you don't offer multiple options, then the smartest thing to do is just accept the request across your entire company until you get another request for communication from that user.
To summarize: Make it easy for people to unsubscribe instantly using whatever method they want, and tell them where to go if they just can't unsubscribe. Doing that will help you with the law, as well as help you build your brand's credibility with your users.