As someone who spends a lot of time thinking about customer loyalty, I'm always surprised by how few loyalty programs take full advantage of email. While nearly every brand issues a "Welcome to our loyalty program" missive, many do little beyond that in the way of targeted, loyalty-powered email campaigns.

Yet data we've collected from clients at 500friends shows that loyalty-powered emails generate up to 50% higher response rates versus regular promotional emails. That's because emails around loyalty deliver relevance and value, and not just another sale or discount. If your brand runs a loyalty program (or if you're thinking about launching one), automatically triggering these emails will boost your engagement metrics and increase the lifetime value of your customers.

1. Lapsed customer offer
Sample subject line: "Just for you: Double rewards this weekend"

When customers haven't purchased for a long time, you're at risk of losing them forever. Set up a triggered email that not only invites them back, but also offers an incentive to return. After how many days of inactivity, exactly, should you send this email? Analyze historical repurchase data to find the point at which customers in your target segments tend to fade away, and make the inactivity trigger period just shorter than that. Experiment with different periods (and offers), measuring the effect on average purchase frequency by segment.

2. Monthly reward statement
Sample subject line: "You have rewards to redeem"

Rewards balance statements give you an opportunity for personalized, non-salesy interactions with your loyalty program members, who tend to be your best customers. They let you establish a cadence of positive communication, and they're great for encouraging rewards redemption, so that customers get the value that your loyalty program was designed to deliver. Also, statements can contain exclusive member offers, which are a benefit of many loyalty programs but can get lost in other communications.

3. Notification that new rewards are within reach
Sample subject line: "You're close to another 10% Savings Certificate"

Letting members know when they're close to new rewards is not only helpful - it can be highly effective at upselling. For example, if a customer has bought $180 worth of merchandise and your retention program rewards every $100 spent with a 10% coupon, send an email reminder that $20 more will trigger the next reward. Do the same when customers are close to reaching higher status tiers.

4. Reward expiration reminder
Sample subject line: "Redeem your rewards before they expire"

Consumers are generally accepting of rewards expiration if the terms are clearly communicated. Expiration reminder emails are a great way not only to add clarity, but also to create a sense of urgency that drives incremental revenue. These emails, too, can include special offers: "Use your rewards this weekend and earn a special loyalty bonus." Ideally, expiration should be triggered by purchase inactivity - a la airline mileage programs. In that case, expiration reminders essentially function as lapsing customer offers (described above).

5. Tier status achievement
Sample subject line: "Congrats on reaching Platinum status"

When customers reach new a new status tier in your loyalty program, make sure they know it. If you have structured your tier benefits correctly, higher status tiers should maximize retention rates among your most valuable customers. This email should showcase new benefits earned, and can include a special offer as a surprise perk. For example: "In celebration of your new status, you'll earn double rewards for 30 days."