Enticed by an in-store promotion at a large retail chain recently, I gave my email address to the cashier in exchange for a perk. A week later, as I was trying to purchase the same item in different colors, I thought it would be easy to find my in-store order on the store’s website and then place a larger order for the item. But after searching my account exhaustively, I realized that my in-store purchase was not linked to my online store account and wondered why the retailer didn’t link my in-store and online profiles as soon as the cashier entered my email. It would have saved me a phone call to the store to get the item’s searchable SKU or even a gratuitous store visit, and I would have been happily placing the larger online order by now.

Collecting email addresses at the point of sale (POS) can give new retailers a surefire way to build an email list quickly and effectively for customer loyalty campaigns. And, for established retailers who have already amassed a large email list, it can provide an indispensable opportunity to link online and offline purchasing history to create deeply personalized experiences at every customer interaction.

To give you an example, let’s say you receive an email from a retailer about a Memorial Day Sale but make a purchase in-store instead of online. The retailer should be able to attribute the sale to the email you received a few weeks earlier. To make this happen, the retailer needs to link your in-store and online identities and learn who you are inside the store by asking for either your email address or your loyalty card at POS.

Although social media seems to be receiving much of the attention today, email marketing is still considered one of the most effective tools for direct marketing. In new customer acquisition, for instance, acquiring email addresses is more fruitful than achieving Facebook likes. When you have a customer’s email address, you can directly engage with that individual in interactive, personalized conversations across multiple channels.

One popular way to get attention is to offer customers personalized discounts, points, and rewards that are relevant to their shopping history. Stadium, the largest retailer in the Nordics, touts a loyalty program with more than 1 million members. The company uses the leading cross-channel campaign management solution to grow its loyalty program by launching cross-channel campaigns at different stages during the customer journey.

In its email campaign, Stadium gives special offers to active customers based on their purchase history and to inactive customers based on their indicated interests. Combining online and offline campaigns successfully, Stadium uses the conversational marketing technology to create personalized letters with customized offers to be inserted in its magazine and e-newsletters—with each offer personalized to the customer based on previous buying history and interests. Stadium also measures offline coupon redemption by using the technology when scanning of unique barcodes at any POS device.

Taking it a step further, once you have the customer’s email address, you can use it to link the customer’s online and offline purchasing history.  Having both customer histories linked can also enable incredibly compelling interactions on your website, mobile app, and in-store. Potentially, for example, when a customer visits a cosmetics department, an in-store employee can be alerted to give distinct sample-sized gifts to that person based on his or her past purchasing behavior. Or in real-time, a shoe retailer can ping both the in-store sales representatives and e-commerce sites about which types of shoes to recommend to a particular customer at any given moment.

Although many large retailers already collect customer email addresses at the counter, the methods aren’t always effective. Typically, cashiers use a form to collect customer information or type the customer’s email address into their POS system. However, collecting the email address or any other customer data by hand can lead to inaccuracies in data collection. Cashiers who are in a rush to complete a transaction do not have bulletproof and consistent ways of recording email addresses accurately or of validating them automatically in real time. Remarkably, according to Direct Marketing Association, for every $1 mar­keters spend on email, the aver­age ROI is $40. Therefore, the more accurate the data is, the more likely it is that your email marketing campaign will lead to higher conversions.

In addition to real-time email address validation, you can incentivize customers to provide valid email addresses by enticing them with free or discounted items in exchange. Alternatively, you can ask for email addresses by adding more value to a deal when a customer makes a large purchase, such as a new computer, by offering an additional 1-month warranty. Once you have the email address, you can engage in a conversation with the customer throughout the relationship.

Providing email receipts is another ingenious way to get an email address and offer convenience. Tablet POS systems such as Square and Revel Systems give us a glimpse of the future of POS systems and their potential power in bringing customers back. In these tablet POS systems, you can give customers the option of having their receipts sent to their email or as a text message. You can then use customers’ email addresses to create customer profiles and measure purchase history immediately. And launching email-marketing campaigns in sync with the customer profiles in your POS system can streamline your offline-to-online marketing, identification of unknown customers, and customer loyalty processes.

Collecting customer email addresses at POS offers many opportunities to deeply personalize and unify your online and in-store shopping experiences. Doing so will set your brand and retail experience apart from your competitors.