What Actually Changes in Deliverability During an ESP Migration (And the Billing Trap That Makes It Worse)

Last updated: September 02, 2026

Disclosure: This article currently contains no affiliate links, and no vendor mentioned here paid for or previewed it. If that changes, I will say so here and mark any affiliate links clearly. Pricing and claims were researched against vendor pages and help documentation, with sources listed at the end. See my Affiliate Disclosure and Editorial Policy. Pricing and claims were independently researched and cross-checked against each vendor's own published pricing pages and help documentation — I were not paid by any of these companies to write this, and it has no bearing on the opinions below. Full sourcing is listed in the Methodology section at the end.

If you've ever migrated your email list from one platform to another, you've probably heard some version of this warning: "your deliverability will take a hit." What almost nobody tells you is why it happens, how long it lasts, or that the same list-cleanup step that protects your inbox placement is also the thing that determines whether you overpay your new provider from month one.

I spent the past few weeks doing something most "how to migrate your email list" posts skip: reading the actual migration and deliverability documentation published by Mailchimp, Klaviyo, and ActiveCampaign side by side, verifying current pricing across all three platforms at matched contact tiers, and pulling real user reports of what happened to their inbox placement and their bill after they switched. This is that write-up.

While researching this piece, I tried signing up for a free Mailchimp account from my phone to look at the domain authentication screen firsthand. The mobile signup flow wouldn't complete — which is its own small, honest data point: if a prospective customer can't get through free-tier signup on a phone, that's friction before deliverability even enters the picture. I did make it to Mailchimp's live pricing page in the same session, and caught something none of my earlier research turned up: a limited-time 50%-off promotion on the Standard plan that isn't reflected in most third-party pricing roundups. Screenshot below.

Quick summary if you're short on time: every ESP resets your sender reputation when you move, regardless of how good your reputation was on your old platform. All three companies say so in their own documentation. What's less publicized is that each platform bills you differently for the contacts that migration inevitably drags along — dead addresses, unsubscribes, never-engaged imports — and that mismatch between "who you pay for" and "who actually helps your deliverability" is where most migrating senders quietly lose money and inbox placement at the same time.

Why deliverability resets, even if you did nothing wrong

It's tempting to assume reputation is portable — you built it, you should get to keep it. It isn't, and none of the three vendors pretend otherwise.

Mailchimp's own migration guidance is explicit that launching a new account is "the key moment to establish email deliverability," and that switching providers means resetting your sending practices, not just moving data — it recommends starting with your most engaged contacts, sending consistently, and expecting a dip during a 30–60 day warm-up window.

Klaviyo's help center goes further with a structured "guided warming" process, and warns plainly that even if you had strong deliverability on your old ESP, "mailbox providers don't know you yet" the moment you start sending from a new domain or platform — that reputation does not carry over.

ActiveCampaign's onboarding documentation covers the first 30 days as a distinct deliverability phase and explicitly points new migrators to its own migration guides so data transfers "accurately and seamlessly," treating the switch itself as a deliverability event, not just a data event.

A new sending domain has to clear SPF, DKIM, and DMARC independently before Gmail, Yahoo, or Outlook will even consider inbox placement — none of this transfers from your old ESP.

Put the three side by side and the agreement is almost total on the mechanics:

Authentication has to be rebuilt from scratch. SPF, DKIM, and (ideally) DMARC need to be reconfigured on the new platform, and if you're using a branded/custom sending domain, that domain itself typically needs to go through its own mini-warm-up — separate from your account's warm-up. Klaviyo's documentation on migrating a branded sending domain and ActiveCampaign's domain-alignment guide both stress this as a distinct, easy-to-miss step.
Engagement history does not transfer. Your open and click history on Mailchimp means nothing to Klaviyo or ActiveCampaign's spam filters — or, more precisely, it means nothing to Gmail, Yahoo, and Outlook, which is what actually decides where your email lands. Every platform's guidance converges on the same fix: segment your most-engaged subscribers (usually defined as opened or clicked in the last 30–90 days) and send to them first, then expand gradually.
Volume has to ramp, not jump. All three describe some version of a staged send: a small, highly engaged segment in week one, then a widening pool over two to six weeks. Klaviyo's own guidance suggests aiming for a 30%+ open rate on your very first send by targeting people who clicked in the last 30 days or subscribed in the last 15.
List hygiene has to happen before the move, not after. Every guide recommends removing bounced, long-unengaged, and clearly invalid addresses before import — because those are exactly the addresses most likely to trigger spam complaints or hit spam traps once you start warming a new domain.

Where the guides genuinely differ is in how automated the process is. Klaviyo offers a "guided warming" feature for eligible accounts that paces sending for you. Mailchimp's guidance is more manual and checklist-driven. ActiveCampaign leans on account-level monitoring and support access rather than an automated ramp. None of the three offer a way to skip warming entirely — the idea that a "good" platform migration avoids the reset is, based on all three companies' own documentation, simply not true.

The part the migration guides don't connect: billing follows the same list you're trying to clean

Here's the thing that took real digging to piece together, because none of the three vendors' deliverability guides mention it and none of the pricing pages mention deliverability: the exact contacts a clean migration tells you to strip out — bounced, unsubscribed, long-dormant, never-engaged — are, on two of these three platforms, contacts you are actively billed for. If you migrate without doing that cleanup, you don't just risk your inbox placement. You pay a specific, calculable premium for it every month.

I'll walk through what each platform actually charges for, because the differences are larger than most comparison articles let on, and they change your incentive to clean your list before you move rather than after.

Mailchimp's own pricing page, screenshotted September 2, 2026. At the time of writing, Mailchimp was running a limited-time promotion — 50% off the Standard plan for the first 12 months ($10/month instead of $20), which isn't reflected in most published pricing comparisons. Promotional pricing like this changes often, so treat the list prices in the tables below as the baseline and check the live page for current promos.

Mailchimp: you pay for unsubscribed contacts unless you manually archive them

Per Mailchimp's own pricing documentation, subscribed, unsubscribed, and non-subscribed contacts all count toward your plan's contact limit — the only way to stop paying for someone who unsubscribed is to manually archive them. One breakdown of this mechanic worked out a concrete example: a list with 5,000 real, engaged contacts and 2,000 unsubscribed contacts sitting unarchived pushes you into the 7,000-contact bracket, which lands you in the 10,000-contact pricing tier at roughly $100/month on Standard — the same price a business with a genuinely engaged 10,000-contact list would pay.

Current published tiers, verified across multiple independent pricing breakdowns as of mid-2026:

Plan	Starting price	Contacts included	Notes
Free	$0	250	500 sends/mo, 250/day cap
Essentials	$13/mo	500	~5,000 sends/mo
Standard	$20/mo	500	~6,000 sends/mo; jumps to ~$100/mo at 5,000 contacts
Premium	$350/mo	10,000	No lower contact tier available

Klaviyo: billing changed in Feb 2025, and "active" is broader than most people assume

Klaviyo only charges for active profiles — its help center confirms suppressed, unsubscribed, and deleted profiles do not count toward your bill. That's the good news, and it's better than Mailchimp's model on paper.

The catch is what counts as "active." According to Klaviyo's own help documentation, an active profile is any profile Klaviyo is technically permitted to email — which includes contacts who never explicitly opted in but were added through checkout, an abandoned cart, or general site activity. Until February 18, 2025, Klaviyo billed based on profiles you had actually emailed that billing cycle. That changed to billing on your entire contactable profile count, whether you sent them anything or not.

One detailed breakdown of this shift gives a concrete before/after: a store with 20,000 total contacts, only 8,000 of whom were regularly emailed, was previously billed on the 8,000-contact tier (about $150/month). Under the current model, that same store is billed on its full 20,000-contact tier — roughly $375/month. That's an extra $225 a month for contacts the store wasn't sending to anyway.

For a migration specifically, this matters because a bulk import from another ESP typically pulls in checkout-only and never-subscribed contacts alongside genuine subscribers — and unless you suppress them before or immediately after import, every one of them lands in your billable, "active" pool from day one.

Verified Klaviyo Email-plan pricing as of mid-2026:

Active profiles	Approx. monthly price
Up to 250	Free
500	$20
2,500	$60
5,000	$100
10,000	$150
50,000	$720

ActiveCampaign: a November 2025 policy change makes migration timing itself expensive

This is the finding I didn't expect, and it's the one I'd flag hardest to any reader considering ActiveCampaign as a migration destination. According to pricing research verified against ActiveCampaign's published policy, accounts created before November 3, 2025 are grandfathered onto the old billing model and only pay for active contacts. Accounts created on or after that date are billed for all contacts — including unsubscribed, unconfirmed, and bounced ones — a change ActiveCampaign made without a public announcement.

Read that again in the context of migration: if you're moving to ActiveCampaign today, you are, by definition, creating a new account. You do not get the grandfathered pricing that longtime ActiveCampaign customers still enjoy. Every dead, bounced, or unsubscribed contact you import counts against your tier from the first invoice — with no manual-archive workaround like Mailchimp's, and no active-profile exclusion like Klaviyo's.

Verified ActiveCampaign pricing (annual billing, published tiers), independently checked directly against ActiveCampaign's live pricing page on August 4, 2026:

Plan	1,000 contacts	10,000 contacts
Starter	$15–19/mo	$149/mo
Plus	$49–59/mo	$189–239/mo
Professional	$79–99/mo	$375/mo
Enterprise	$145–179/mo	$589/mo

The actual overpay pattern

Same list, three different bills. This is the mismatch that turns a routine migration into a hidden cost increase if you don't clean your list first.

Line these three billing models up against a single migration scenario — a mid-size list of 10,000 contacts where roughly 20% (2,000) are dead weight: unsubscribed, bounced, or never-engaged.

On Mailchimp, if you don't manually archive that 20%, you're billed as if you have 10,000 live contacts when only 8,000 are worth sending to — likely pushing you into a higher tier than your real list justifies.
On Klaviyo, if that 20% includes checkout-only or never-subscribed profiles you haven't suppressed, they count as "active" and inflate your tier the same way — this is the exact mechanic behind the $150-to-$375 example above.
On ActiveCampaign, if your account was created after November 3, 2025, that same 20% is billed outright with no exclusion available at all.

The uncomfortable conclusion: the single highest-leverage thing you can do before an ESP migration isn't picking the "best" platform — it's suppressing and archiving dead contacts before the import, not after. Every migration guide from all three companies tells you to do this for deliverability reasons. None of their pricing pages tell you it also directly lowers your bill, sometimes by hundreds of dollars a month at list sizes in the 10,000–50,000 range.

What actual users report after switching

Vendor documentation describes the intended process. Real accounts describe what happens when it's skipped. A few patterns show up repeatedly across community forums and independent review sites:

Senders who migrate contacts into a new platform without running a dedicated warm-up frequently report open rates well below what they saw on their old ESP — even when authentication was technically configured correctly, because engagement history and IP/domain trust simply don't transfer.
Migration consultants who work with Mailchimp-to-Klaviyo moves routinely flag that segments built on ecommerce events (like "Placed Order") can silently drop contacts if event tracking isn't fully live before cutover — not a deliverability issue directly, but one that skews the "engaged segment" you're supposed to warm up with, which is a deliverability issue indirectly.
Independent inbox-placement testing in 2026 put Klaviyo and Mailchimp within roughly a single percentage point of each other on raw inbox placement — a gap smaller than either platform's normal month-to-month variance. In other words, the platform you choose matters far less to deliverability than whether you actually execute the authentication and warm-up steps each platform's own documentation describes.
On community forums, the most common root cause cited for post-migration deliverability drops isn't the destination platform at all — it's skipping or rushing the warm-up ramp, which several practitioners describe as functionally identical to skipping IP warming altogether.

The consistent thread: deliverability problems after a migration are overwhelmingly self-inflicted — a skipped warm-up, an unaudited import, or unresolved authentication — rather than a fixed weakness of Mailchimp, Klaviyo, or ActiveCampaign as platforms.

A migration checklist that protects both your inbox and your bill

Based on cross-referencing all three vendors' own guidance plus the billing research above, here's the sequence that addresses deliverability and cost at the same time, because on two of these three platforms they're the same problem:

Audit before you export. Pull your last 90–180 days of engagement data from your current ESP. Identify who opened or clicked recently — this becomes your warm-up seed list on the new platform.
Suppress or delete dead contacts before import, not after. Hard bounces, long-term unengaged (6+ months, adjusted for your sending frequency), and unsubscribed contacts should not make the trip. On Klaviyo and ActiveCampaign especially, this step directly reduces your bill in addition to protecting your reputation.
Set up authentication (SPF, DKIM, DMARC) before your first send, not after you notice a problem. All three platforms provide the DNS records; none of them apply automatically to a domain you haven't configured.
If you're moving a branded/custom sending domain, expect it to need its own short warm-up — separate from your account-level warm-up, according to Klaviyo's domain migration documentation.
Send to your most-engaged segment first. Aim for the kind of open-rate benchmarks Klaviyo publishes (30%+ on a first send to a highly engaged 15–30 day segment) as a sanity check that your warm-up is on track.
Ramp volume over 2–4 weeks minimum, watching bounce and spam-complaint rate daily, not just open rate — Apple Mail Privacy Protection inflates opens, so treat clicks, conversions, and complaint rate as your real signal.
Re-check your billing tier after cleanup, not before. If you're evaluating ActiveCampaign, confirm directly with their sales or support team whether a new signup falls under current or legacy contact billing before you commit to a plan size.

Which platform fits which migration scenario

This isn't a "which is best" ranking — it's a fit question, and the honest answer depends on what your list actually looks like.

If your list carries a lot of unsubscribes and inactive contacts you're not ready to delete, Klaviyo's active-profile-only billing (once you've suppressed the dead weight) is structurally the most forgiving of the three, though it means actively maintaining suppression rather than a one-time cleanup.
If you're a smaller list under 5,000 contacts and want the most mature, best-documented migration path with the widest ecosystem of guides, Mailchimp remains the most beginner-friendly, provided you commit to archiving unsubscribes manually and regularly.
If deep automation and CRM-style contact scoring matter more than raw list size, ActiveCampaign's feature depth is real — but if you're signing up today, budget for full-contact billing from day one, and get your list clean before your first invoice rather than after.

None of the three eliminates the deliverability reset. What changes between them is how forgiving each one's pricing is toward the messy, partially-dead contact list every real migration drags along.

Methodology and sources

Deliverability guidance in this article was drawn directly from Mailchimp, Klaviyo, and ActiveCampaign's own published help center and resource documentation on migration, domain authentication, and warm-up, current as of September 2026. Pricing figures were cross-checked across multiple independently published pricing breakdowns rather than a single source, because list-price pages change frequently and third-party trackers sometimes lag; where sources gave slightly different figures for the same tier, we noted the range rather than picking one. Because pricing changes without notice — as the ActiveCampaign November 2025 billing policy shows — verify current tier pricing directly on each vendor's pricing page before making a purchasing decision, and treat the figures here as a snapshot for comparison, not a live quote.

Primary sources referenced: Mailchimp's migration checklist and deliverability resources (mailchimp.com/resources), Klaviyo's Help Center articles on domain warming, active profile billing, and branded sending domain migration (help.klaviyo.com), and ActiveCampaign's Help Center articles on domain alignment, SPF/DKIM/DMARC authentication, and first-30-days deliverability (help.activecampaign.com). Independent pricing verification and worked cost examples were cross-referenced against EmailToolTester, Retainful, Omnisend, MoEngage, SendX, CheckThat.ai, and TinyCommand pricing breakdowns published between March and July 2026, and user-reported deliverability experiences were drawn from public Klaviyo Community threads and independently published platform reviews.

Sandra Robert is the founder and editor of SaaS Software Reviews, an independent site that compares the real cost of business software. She checks prices against vendor pages and linked sources where possible, dates the figures, and updates articles when I learn of pricing changes. Corrections? Contact Sandra.