- Require registration for site access for special bonus content. Many newspaper sites require this nowadays. Whether or not you're a fan, it does indeed drive some significant number of folks to register and receive emails. Be sure you use confirmed opt-in (double opt-in) or else you're just going to get a bunch of junk addresses. Also be sure to require the double opt-in confirmation before giving away the content. Otherwise the opt-in confirmation rate will be much lower. People don't put the quarter in if they've already received the candy.
- Invite visitors to register in exchange for a free product or download (white paper, how-to document, e-book, a free trial version of a software program). I used to manage a system that handled double opt-in signup registrations for free trial software downloads. I know this one works well.
- Use paid search advertising driving to a signup page on a particular topic or keyword. It seems to be a popular list growth method for online casinos, but I see a lot of other types of companies do this as well. If you're on topic and your newsletter or list is on topic, people will want to sign up. It'd all be people who are actively interested in your topic or product.
- Be sure to link to a newsletter signup form on every page on your website. It should be part of a site's navigation. Every page you show to a visitor, somewhere there should be a signup form or link. Don't make potential subscribers have to hunt for the front door to your email list.
- Include messaging around the signup process, recommending that subscribers join the list now for important email relating to X, where X is your specific product or feature you're going to highlight in your email communication. Or, "Want to know when our product goes on sale? Sign up and we'll let you know via email."
- Implement an opt-in email signup process for inbound call center communication. If a consumer calls in with an order or question, invite them to provide an email address so that they can receive followup email. Definitely validate this with double opt-in, to deal with call center rep typos and funny stuff, as well as ensuring subscriber permission. The value here is that opening an email communication channel means you've got a chance to converting an offline buyer to an online buyer. It's usually cheaper for a company to sell to a consumer online than via a phone call to a call center rep.
- Implement a subscriber signup process at brick-and-mortar (in store) POS (point of sale). Invite a customer to provide an email address during that process. Be sure that sales reps are trained to explain exactly what the subscriber is signing up for. And be sure that this feeds into a double opt-in process. Even though the offline nature of the signup can mean a delay before the confirmation email is received, if you don't properly confirm these addresses, you'll find yourself in a world of hurt. Using this process without double opt-in was previously highlighted by anti-spam blacklist group Spamhaus as a primary factor driving blacklistings of big retail brands a few years ago. It's a time I don't want to revisit and neither do you.
- Hey customer, do you want to receive warranty updates, a copy of your email receipt, or other transactional messages? Register here. Offer an opportunity to opt-in to other types of communication at the same time.
- Ethical list swapping. Don't ever give your email list to someone else. It'll get loose and people will hate you for causing them to get spammed. Instead, what you do is send mail to your own list as you normally would do. In that email, invite people to click to opt-in to the other organization's list. If it's Bob and Mike, you'd have Bob send an email to Bob's list with a "Click here to sign up for Mike's list." Only the people that click should be shared with Mike.
- Direct Co-reg. Co-registration can be icky, as some people call it "co-reg" when they really mean "buying email addresses without any sort of explicit permission." But there's an ethical way to do it. Some free offer or game sites will provide subscribers with an opportunity to sign up for email messages from partner companies. Make sure you're explicitly listed as a partner company, with an opt-in checkbox specifically for your site's emails. Double opt-in and tracking is king here. Test and monitor the process-- don't assume that you can trust a vendor based only on what they say. Sadly, I've seen vendors feed in old addresses and pretend they're new signups. If you have a double opt-in process, this becomes obvious as the confirmation rate drops off when that happens. And you're protected against being labeled a spammer.
I talk about double opt-in in some of these, and for the others, it can almost become a religious argument as to whether or not you should be using double opt-in. But if you fully implement double opt-in, aka confirmed opt-in, you are best positioned to avoid getting smacked down by an ISP or blacklist group for mailing to spamtrap addresses that were either typo'd accidentally or maliciously into your signup forms. If you do it now, you won't get subject to potentially brutal list cleanup requirements later.
And whatever you do, don't mine your LinkedIn network for list building purposes. It's spammy and stupid. Don't invite your subscribers to upload their address books, either.