Marketers should create temporary, high-energy events rather than long-term, low-engagement communities. A time-bound "24-hour vault unlock" or a 30-day pop-up group generates urgency and a fear of missing out, driving significant participation that permanent online spaces often fail to sustain, even in "boring" industries.

Using subject lines like "Verify your active status" can lift open rates by 27-31% for contacts who haven't engaged in over a year. While effective for reactivation, this slightly gimmicky approach will also annoy some users, leading to a higher-than-usual unsubscribe rate and negative replies, which requires 'thick skin'.

For B2B re-engagement, a highly effective subject line is "Are you still with [Company Name]?". This personalizes the email at scale by dynamically inserting the contact's employer. It grabs attention and prompts an open to confirm or update their status, successfully re-engaging them with your content or offers.

From Nov 20th to Dec 20th, sending a personal letter-style email from a founder or executive to unengaged contacts can increase open rates by 40%. The key is changing the "from name" to a person, not the brand, and using a subject line that acknowledges their absence. This strategy works for both B2B and B2C brands.

Counterintuitively, Duolingo discovered that competitive leaderboards are more engaging when users are pitted against strangers at a similar commitment level. Competing with friends often fails because their dedication rarely matches, making the competition feel unbalanced and demotivating.

When a prospect goes silent on your primary channels (email, work phone), they may be subconsciously filtering you out. Break this pattern by using a novel channel like WhatsApp or a different phone number. This can bypass their filters and elicit a response.

To amplify word-of-mouth, Duolingo identified existing sharing behavior by temporarily tracking user screenshots. They found hotspots like streak milestones and funny challenges, then invested in designers to make these moments even more shareable.

A key viability metric for consumer subscription apps is achieving 30-40% Day 1 retention. Anything lower suggests a fundamental product-value mismatch, making it mathematically difficult to acquire enough users to build a sustainable active user base.

After reaching scale, a product's dormant user base is a massive growth opportunity. Activating these users requires designing specific return experiences, like Duolingo’s proficiency tests, which can be a bigger lever than new user acquisition.