Email list decay

The uncomfortable truth about every email list: it's a leaky bucket

Most marketers see their Klaviyo or HubSpot dashboard showing "82,000 subscribers" and think the list is growing because the number went up this month. The actual number of engaged, revenue-producing subscribers is almost certainly shrinking in a way the dashboard hides. A typical DTC email list loses 22–38% of its engaged subscribers each year to hard bounces, passive unsubscribes (people who ignore everything), explicit unsubscribes, spam complaints, and inbox-provider suppression (Gmail actively hides unengaged senders after a while).

If your list is gaining 3% in new subscribers monthly but losing 2.5% in decay, you're net positive on total list size but the revenue-per-subscriber is dropping because the engaged core of the list is thinning out. This calculator models that decay explicitly — so you can see whether your steady-state list size matches your target revenue contribution.

Benchmarks: decay rates across categories (2026)

The four decay mechanisms you need to model separately

1. Hard bounces and invalid emails. 0.5–2% per month. Once an email bounces hard, it's gone — delete it from the list. Keeping hard-bounces in your "engaged" list is inbox-placement suicide; Gmail and Outlook watch bounce rates as a primary sender reputation signal.

2. Explicit unsubscribes. 0.2–0.5% per campaign. The explicit "unsubscribe" clickers are at least being honest. Multiply by your campaign frequency: 4 campaigns/month × 0.35% = 1.4% monthly list loss to explicit opt-outs.

3. Passive disengagement. The big one. A subscriber who hasn't opened in 90+ days is statistically gone — they just haven't unsubscribed. On Klaviyo and HubSpot, these accumulate in your "active" count while contributing zero revenue. 2–4% of your list moves from engaged to passive every month.

4. Spam complaints. 0.02–0.2% per campaign. Over 0.3% in any single send and Gmail will throttle your domain reputation for 2–4 weeks. Keep this below 0.1% per campaign always.

The steady-state math: how big does your list have to be?

If you lose 3% of your engaged list per month and you gain 3% per month from signups, you're at steady state — but a steady-state list is only as big as your acquisition rate allows. Working backward:

Target monthly email revenue: $200K. Revenue per engaged subscriber per month: $2.80 (this varies by category — check yours). Required engaged subscribers: 71,400. At 35% annual decay, you need to add 71,400 × 0.35 = 24,990 new engaged subscribers per year, or roughly 2,080 per month just to stay flat.

If your current acquisition rate is 1,200 new engaged subs per month, your list is shrinking toward a steady state of about 41,000 engaged subs — which would produce only $115K/month in revenue, down 42% from target. This is what "the list is still growing" looks like while revenue erodes.

Sunset flows: the controversial but correct move

The counterintuitive advice that saves most email programs: regularly suppress unengaged subscribers. A "sunset flow" automatically moves subscribers who haven't opened in 120–180 days into a suppressed list. You still have their address, but you stop sending to them.

This reduces list size by 20–40% at first. It also typically lifts open rates by 30–80% and click rates by 50–120% within 60 days, because your inbox placement improves dramatically. Klaviyo's internal data shows brands that aggressively sunset produce 2–3x more revenue per subscriber than brands that don't.

The emotional obstacle is the "we paid to acquire these subscribers" objection. Answer: they've already stopped opening. You're not losing them by suppressing — you're recognizing a loss that already occurred, and the benefit is better delivery to the engaged core.

Acquisition source quality: not all subscribers decay equally

Where a subscriber came from predicts their decay curve:

Shift acquisition mix toward post-purchase, welcome-series pop-up, and topical lead magnets. Every dollar spent acquiring low-quality contest subscribers is a dollar that creates decay, not revenue.

The deliverability tax that compounds with decay

Unengaged subscribers hurt your inbox placement for everyone else on the list. When you send to subscribers with no open history, Gmail and Outlook interpret that as low-engagement mail and throttle your domain — which reduces open rates on subscribers who would have opened otherwise. The math: if 40% of your list is unengaged and you send to them, your effective open rate on the engaged 60% drops from 35% to 22% because of deliverability degradation.

Suppress aggressively. Watch your sender-reputation scores in Google Postmaster Tools and Microsoft SNDS. Keep your active segment tight — the revenue math almost always favors a smaller, hotter list over a larger, colder one.

Re-engagement campaigns: when they work and when they don't

A re-engagement flow ("We miss you! Here's 20% off") sent to 180-day lapsed subscribers typically re-activates 3–8% of them. That's better than zero. But if you send a re-engagement to subscribers who haven't opened in 12+ months, re-activation drops below 1% and you get a spike in spam complaints that torches deliverability for 2–3 weeks.

Cap re-engagement attempts at the 90–180 day window. Anyone past 180 days: suppress and move on. You can resurrect them later with a double-opt-in campaign tied to a major launch — but only once, and only with an explicit re-opt-in CTA.

The monthly dashboard that prevents this problem

• Total list size. Sanity number, least important.
• Active engaged subs (90-day opener). The real KPI.
• Monthly new-sub count by source. Not just total — by source, because quality varies.
• Monthly decay count (sunsetted + hard bounced + unsubscribed). Plot against new subs.
• Revenue per engaged subscriber (RPES). Trend monthly; if declining, deliverability or content is the issue.
• Inbox placement rate. Pull from GlockApps or Litmus quarterly.

Three list-decay archetypes with steady-state math

Archetype 1: DTC beauty brand, 95K total list, 54K engaged

AOV $78, email attribution at 28% of revenue = $3.8M annual email revenue. Revenue per engaged subscriber per year = $70. Monthly new subscribers: 2,400 (1,800 from pop-up at 6% signup rate on 30K sessions/mo, 400 from post-purchase opt-in at 42% conversion on 950 orders/mo, 200 from back-in-stock and other flows). Monthly decay: 3.2% of engaged base = 1,730 lost per month. Net growth +670 engaged subs/mo — healthy. Steady-state projection at current acquisition rate: 75K engaged = $5.2M email revenue ceiling. To grow past that, either push pop-up conversion rate from 6% to 9% (Justuno or Privy at $29–$399/mo) or open a second-step SMS capture to recover email non-converters.

Archetype 2: B2B SaaS, 180K total list, 62K engaged

Mid-market B2B analytics tool. HubSpot Marketing Hub Pro ($800/mo). Monthly nurture campaigns + event invites + blog digest. Monthly new contacts: 1,100 (content downloads 600, webinar signups 300, demo-request overflow 200). Monthly decay: 2.1% = 1,300 lost to job changes (LinkedIn job-change detection via Clearbit webhook, $30K/year), unsubscribes, and passive disengagement. Net shrinking by 200 engaged subs/mo — a red flag nobody noticed for 8 months. Fix: added a quarterly re-engagement flow triggered at 90-day no-open (not 180), improved subject-line testing using Phrasee ($500–$2,000/mo), and rebuilt the blog-digest template with better segmentation. Engaged base recovered to +350 net growth/mo within 5 months.

Archetype 3: Publisher / newsletter, 240K subscribers, 155K engaged

Ad-revenue supported newsletter, 3 sends per week. RPES (revenue per engaged sub per year) $11 via banner ads + sponsored placements. Monthly new subs: 5,800 (Substack referral bonus, cross-promotion with 3 partner newsletters at $1,500–$4,500 per swap via SparkLoop at $249–$999/mo, organic Twitter/LinkedIn). Monthly decay: 1.9% = 2,950 lost. Net growth +2,850 engaged subs/mo. Sunset policy: 90-day no-open flushes to suppressed state. Aggressive deliverability hygiene: daily bounce cleaning, DMARC at reject, BIMI logo live. Inbox placement rate at 96.3% (GlockApps weekly check). This is what a well-run decay discipline looks like — the cost is $18K/year in tooling, the value is an extra $280K/year in ad revenue vs. a similar-size list that is not disciplined.

Email decay tool-stack reference (April 2026)

Decision framework: when to sunset, when to re-engage, when to suppress permanently

Sunset (move to suppressed state) when a subscriber has not opened or clicked in 120–150 days for DTC, 180 days for B2B SaaS, 90 days for publisher/newsletter. Re-engage (one-shot winback flow with strong offer) at the 90–120 day window; after one attempt with no response, sunset. Suppress permanently any subscriber who has hard-bounced twice, triggered a spam complaint, or been unsubscribed for over 24 months. Before any large re-activation campaign, warm up the send: start at 5% of the cold list, grow to 25% over 14 days, watch Gmail Postmaster sender reputation daily, and halt immediately if reputation drops below 70 on their scale. The whole decay discipline pays off in two places — higher revenue-per-engaged-subscriber as deliverability improves, and lower list-acquisition pressure because you are not fighting against a leaky bucket. Pair this with Email ROI to see the full revenue impact.