The Lemlist Deliverability Problem at Scale (and How to Fix It Without Switching)

Lemlist built one of the better cold email senders in the market. The personalization tokens, the dynamic landing pages, the campaign builder UX — all of that is real engineering and worth the subscription if you use them.

What Lemlist doesn't build is the infrastructure underneath your mailboxes. Your sending IPs, your domain reputation, your DNS authentication, your warmup network — those are bought from third parties, bundled into the Lemlist subscription, and shared across thousands of other Lemlist customers.

That shared layer is where Lemlist users hit their deliverability ceiling. The fix isn't to leave Lemlist. The fix is to swap the infrastructure for dedicated-per-customer infrastructure and keep Lemlist as the sender on top.

The 30-second answer

The pattern: Lemlist the application works. The infrastructure tier Lemlist routes through is what's broken at cold-email scale.

How Lemlist's stack works (what's theirs, what's not)

Lemlist's product is the campaign manager + personalization engine + unified inbox + warmup network membership. That's what their team builds and maintains.

What Lemlist uses (but doesn't fully control):

• The mailboxes themselves — connected from your Google Workspace, Microsoft 365, or third-party SMTP. Lemlist authenticates against them but doesn't operate them.
• The sending IPs — when you use Lemlist's bundled SMTP, those IPs come from a shared pool. Other Lemlist customers send through the same IPs.
• The DNS / SPF / DKIM / DMARC setup — Lemlist documents what to add but doesn't provision it on your domain.
• The Lemwarm warmup network — Lemlist-managed, shared across thousands of users. Useful, but the shared network's signals get noisy at scale.

The shared parts are fine at low volume. Past ~150 mailboxes, the cracks show.

The Google Workspace + Lemlist combo (most common, hits walls fastest)

The most common Lemlist setup pairs it with Google Workspace mailboxes ($6/user/month × N mailboxes). Lemlist sends through Gmail's SMTP as if you were sending from your own Gmail account.

This works fine at modest scale. Past a few hundred mailboxes, three things start to break:

1. Google Workspace's daily limits become the constraint. 2,000 outbound recipients/day per paid user. At cold email's 2-sends-per-mailbox/day cadence (which is what ColdRelay enforces specifically because higher volume tanks deliverability), the limit isn't the bottleneck. But at higher rates, you hit it.

2. Domain reputation pools across all senders on your workspace domain. If multiple campaigns share one Workspace domain, one bad campaign drags down everyone's reputation. There's no isolation.

3. Workspace suspension risk. Google's TOS prohibits "spam-like" sending behavior — and cold email IS spam-like to their classifier, regardless of intent. Past a certain volume, individual accounts (or the whole tenant) can get suspended. Recovery takes days; sometimes accounts don't come back.

The cost math gets bad too: 500 mailboxes × $6/mo = $3,000/month just for Workspace user licenses, before Lemlist subscription or list cost. The infrastructure isn't even isolated for that price.

The Lemlist-bundled-SMTP problem (different ceiling, same outcome)

The alternative — Lemlist's bundled SMTP provisioning — has a different but parallel issue. Multiple customers send through the same SMTP infrastructure. Sending IPs are shared. One customer's bad campaign — over-aggressive ramp, untargeted list, complaint spikes — drives down the IP's reputation for everyone using it.

You can be doing everything right and watch your inbox placement collapse because of someone else's mistake on the same IP block. This is the neighbor problem; you don't control your neighbors, and you wear their reputation.

Diagnostic test: open Google Postmaster Tools, check IP Reputation. If you see "Medium" or "Low" when you know your own sending is clean, you're sharing an IP with bad actors. (How to read Postmaster Tools →)

How to know if Lemlist's infrastructure is your bottleneck

Five diagnostic signals. Two or more = you're hitting the wall:

1. Inbox rate at 50 mailboxes was 85%+; at 200 mailboxes it's 60% or below. The classic shared-infrastructure scaling curve. Individual mailboxes test fine; the pool tests bad.

2. Reply rates dropped while open rates stayed the same. Counterintuitive but diagnostic. Opens often come from spam-folder skim-readers. Replies require landing in primary inbox and feeling legitimate. Same opens + fewer replies = more spam-folder placement.

3. Google Postmaster Tools shows Domain Reputation drift from High to Medium. Read it directly in Postmaster Tools. Without a content change, that drift means infrastructure-side reputation is sliding.

4. SMTP "temporary deferral" errors on a meaningful percentage of sends. Lemlist's logs will surface these. A few percent is normal. Double-digit percent means receivers are starting to throttle you.

5. Bounce rate creeps above 2% despite list quality being stable. Reputation-driven rejection codes look like bounces but are infrastructure problems wearing list-quality clothing. (Why bounce rate matters →)

The fix: dedicated infrastructure under Lemlist

The architecture is a clean split:

The two layers compose. Lemlist becomes the campaign manager (which it's good at). ColdRelay becomes the deliverability backbone (purpose-built for it). You don't lose Lemlist's UX; you gain the infrastructure layer Lemlist doesn't operate.

The migration: keep Lemlist, swap the infrastructure

Concrete steps:

1. Provision domains + mailboxes through ColdRelay. Setup takes 2 to 4 hours, fully automated — domains purchased, DNS configured, IPs provisioned, mailboxes ready to authenticate.
2. Push the new mailboxes into Lemlist. Lemlist supports adding custom SMTP/IMAP mailboxes directly; ColdRelay's dashboard exports a Lemlist-formatted CSV or pushes via Lemlist's API if you've connected your key.
3. Migrate active campaigns to the new mailboxes (or run new campaigns alongside while old ones finish — Lemlist handles parallel mailboxes fine).
4. Pause sending on the old infrastructure for 7 to 14 days while the new domain reputation builds. ColdRelay's per-customer isolation means the new domains don't inherit any reputation from old shared-pool history.

Cost math compared to Google Workspace + Lemlist's bundled add-ons:

The deliverability lift comes on top of the cost reduction. Same Lemlist subscription, same Lemlist campaigns, ~90% lower infrastructure cost, dedicated-IP-level reputation control.

What about Lemwarm?

Lemwarm is Lemlist's built-in warmup network. Useful for the first few weeks of a brand-new domain, when any warmup signal helps. At scale, the shared-network signals dilute and ColdRelay's infrastructure-level warmup (which runs at the SMTP layer using your dedicated IP) is more targeted.

You can run both in parallel — Lemwarm contributes to the warm-up email exchange volume, while ColdRelay's infrastructure-level warmup makes sure the IP and domain history accumulate cleanly. No conflict.

FAQ

Will I lose my Lemlist campaigns or templates?

No. Lemlist data — campaigns, sequences, templates, personalization tokens, lead lists, unified inbox history — all stays in Lemlist. You're only changing which mailboxes Lemlist routes through.

Does Lemlist support custom SMTP/IMAP mailboxes?

Yes. Lemlist has a "Custom email provider" option in their mailbox connection flow. You enter the SMTP/IMAP host, port, username, password — same as you would for any third-party provider. ColdRelay's dashboard generates these credentials per mailbox and exports them in Lemlist's CSV format for bulk import.

How long until I see the deliverability improvement?

7 to 14 days for the first signal (Domain Reputation in Postmaster Tools stabilizing at High). Reply-rate improvement typically lands in week 3 to 4 as the new mailboxes' reputation matures and the old infrastructure stops dragging averages down.

What if I'm only using Lemlist for personalization, not for warmup or analytics?

Even better. The migration is simpler — connect the new mailboxes, retarget your campaigns, done. ColdRelay's per-mailbox engagement data shows up in your dashboard too if you want it.

Can I A/B test old infrastructure against ColdRelay?

Yes. Most customers run a parallel split for the first 30 days — old campaigns continue on old infrastructure, new mailboxes provision on ColdRelay, traffic gradually shifts. No hard cutover required. Side-by-side reply-rate data lets you verify the lift before fully migrating.

What about other sending tools — Smartlead, Instantly, EmailBison, Saleshandy?

Same pattern. ColdRelay has one-click push integration with Smartlead, Instantly, EmailBison, and Saleshandy. The infrastructure layer underneath is identical regardless of which sender sits on top.

Is there a contract or commitment?

ColdRelay's billing is monthly. The pricing tier you're on (based on mailbox count) updates automatically as you scale up or down. There's a 95% deliverability guarantee with refund in your first 14 days — if the infrastructure doesn't hit that bar, you're out at no cost.

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Lemlist is a good campaign manager. Pair it with infrastructure that's purpose-built for cold email at scale, and the deliverability ceiling moves out by an order of magnitude.

See ColdRelay + Lemlist in action → Try ColdRelay free · Test your current setup → Free deliverability test