The short version: Two independent 60–90 day tests found virtually identical reply rates between the platforms — the real difference is cost structure and what you're trying to do. Instantly wins on volume and price. Lemlist wins on personalization depth and multichannel. Neither platform dramatically outperforms the other on raw reply rate.
What the actual tests found
Two third-party tests ran both platforms head-to-head on the same lists, and the reply-rate results are closer than the marketing suggests:
- Puzzle Inbox (60-day test): Lemlist 4.3% reply rate vs. Instantly 3.9% — a small gap that Puzzle Inbox attributes to Lemlist's personalization features, not a platform-level edge.
- Cotera (90-day test, 1,800 leads per platform): Lemlist 4.0% vs. Instantly 3.7% — a five-reply difference that a proportions test confirmed was statistically indistinguishable from random variation (p = 0.63).
Importantly, the two tests actually point in opposite directions on which platform edges out the other — Puzzle Inbox had Instantly slightly ahead on deliverability metrics while Lemlist led on reply rate; Cotera also had Lemlist narrowly ahead on reply rate. Neither difference is meaningful enough to call a winner on performance alone.
The 23% figure you may have seen floating around is not a Lemlist-vs.-Instantly result. It's the reply-rate lift that Puzzle Inbox observed when comparing personalized-image emails against plain-text emails — a feature advantage that Lemlist offers and Instantly doesn't, but a different claim entirely.
For deliverability, Cotera's 90-day test found Lemlist averaged 84.9% inbox placement vs. Instantly's 82.7% — a marginal difference. Neither platform introduced meaningful bounce issues (2.2% Lemlist vs. 2.4% Instantly on the same list).
According to Instantly's own benchmark report — which, worth noting, is vendor-produced data — the average cold email reply rate across their platform sits at 3.43%, with top performers exceeding 10%. That's a useful baseline for calibrating expectations, but take it with the appropriate grain of salt.
Where the real difference shows up: cost
Cotera's 90-day test used a 3-person SDR team with 6 mailboxes per platform. Over those 90 days, they spent $231 on Instantly and $621 on Lemlist — nearly 3x the cost for comparable performance at that team size. That cost gap is specific to a small-team setup and scales differently depending on how many inboxes and seats you're running.
Here's why the math diverges so quickly at scale: Instantly charges a flat rate per workspace regardless of team size. Lemlist charges per user. Cotera's three-person team on Instantly's Hypergrowth plan cost $77/month total; the equivalent Lemlist setup at $69/seat came to $207/month.
At 30 inboxes, per Puzzle Inbox's analysis, Instantly runs roughly $77.60/month. Getting equivalent inbox capacity on Lemlist — where the Email Pro plan covers 3 sending emails per user at $63/user/month on annual billing ($79/user/month billed monthly), with additional inboxes at $9/email/month — pushes total cost to $300–400+ per month. If you're comparing sticker prices, always make sure you're on the same billing cadence.
Feature differences that actually matter
This is where the platforms genuinely diverge:
- Personalized images: Lemlist only. Inserting a screenshot of a prospect's website with their name overlaid creates a "wow" effect that plain-text emails can't replicate — and Puzzle Inbox's testing found a 23% reply-rate lift from personalized-image emails vs. plain-text. Setup takes 30–60 extra minutes per campaign.
- Multichannel sequences: Lemlist only. Email + LinkedIn connection requests + LinkedIn messages in a single workflow. Instantly is email-only; you'd need a separate tool for LinkedIn.
- Unlimited email accounts: Instantly only. Every plan. Lemlist limits sending emails by tier and charges per additional inbox.
- Lead databases: Lemlist includes a 600M+ leads database on the Email Pro plan. Instantly's database sits at 160M+. On raw database size, Lemlist is actually larger — something the Instantly-vs.-Lemlist narrative often glosses over.
- Warmup networks: Puzzle Inbox puts Instantly's warmup network at roughly 1 million accounts vs. Lemlist's ~100K (Lemwarm). Note that Instantly's own blog cites a 4.2M private network figure — numbers vary by source.
- CRM built-in: Instantly only. Lemlist relies on integrations.
Which one should you pick?
Pick Instantly if: You're running 20+ inboxes, volume is the strategy, you want the simplest possible workflow, flat pricing matters, or you need a built-in CRM. The cost advantage at scale is real and compounds fast.
Pick Lemlist if: You're targeting senior decision-makers who respond to personalization, you want email + LinkedIn in a single workflow, your campaign volume is moderate (under 20 inboxes), or reply quality matters more than reply quantity. The per-seat pricing is easier to justify when you're actually using the personalization and multichannel features.
The honest take: If you're an agency owner running 6 inboxes with a small SDR team, Instantly gets you equivalent results for about a third of the cost. If you're running executive-targeted sequences where a personalized image or LinkedIn touch can break through, Lemlist's premium buys you real differentiation. Most teams should start with Instantly and layer in Lemlist for high-value segments.