Migration timelines in these interviews generally rise with organizational complexity. Smaller brands on straightforward stacks describe moves completed in weeks; mid-market moves take a season; large, multi-brand organizations report projects lasting a year, sometimes more. The ranges overlap, and the same platform can be quick to implement in one environment and slow in another. What they share is the slip: among companies that gave both a plan and an outcome, none finished early. The reasons repeat across vendors, and they are rarely the platform was hard to switch on. Here are the seven — the companion reads are what ESP buyers wish they'd known, where the ratings live, and why companies switch ESPs.
The seven reasons they slip
The data has to be connected before anything sends
The reason buyers cite most is the data behind the email: customer records, product feeds, events and the systems that hold them. “Anytime you onboard a new ESP, there's a ton of data engineering work that needs to happen,” one buyer says, and another, after a move, that “We have a very complex data system. So the migration itself was very challenging.” Poor data carried over becomes cleanup afterwards. Buyers on simple, natively integrated stacks describe the opposite experience, which is why the same platform can take weeks for one company and months for another.
Named in this context: Braze · Listrak · Salesforce Marketing Cloud · Dotdigital
The implementation team sets the pace
Who runs the migration matters as much as the platform. Some buyers were pointed to outside partners rather than the vendor — “They said, you can go talk to these third parties to help you implement,” one says of a platform it evaluated — and describe paying a partner on top of the licence. Others describe vendor teams without the capacity the project needed: “I think sometimes they just don't have enough people on the implementation team who are able to do the things we need to move the project along.” The fastest migrations here are the ones where the vendor ran a calendar-based project plan.
Named in this context: Salesforce Marketing Cloud · Braze · Ometria · Bloomreach
Sender warming can add weeks to the migration
Buyers moving to new sending infrastructure describe gradually increasing email volume to establish sender reputation, often allowing four to six weeks. The requirement and its length depend on the company's sending history, domain and IP set-up, audience size and the new provider's infrastructure: some migrations need a substantial warm-up, others a shorter ramp-up, and some none at all. “There's processes which just take time, like IP warming,” one buyer says. It is the part of the timeline no amount of staffing shortens, and some buyers describe it as the reason they have not switched at all. None here reports an actual drop in deliverability after moving; warming is planned for as a cost and a risk.
Named in this context: Braze · Klaviyo · Listrak · Iterable
Rebuilding flows to parity takes longer than moving the list
Moving subscribers is quick; rebuilding the automated programs that ran on the old platform is not. “To reach parity, from what we had before, to actually getting Braze up and running, it took months,” one buyer says, and another describes two to three months “with the migration, so really rebuilding everything.” Until parity, some companies run campaigns on both platforms — “we had to do one campaign on both platforms, which led to a myriad of troubles and issues for us” — and pay for both.
Named in this context: Braze · Salesforce Marketing Cloud · Bluecore · Zeta
Contract dates set the window
The old contract's end date decides how much time there is, and it cuts both ways. Some buyers renew rather than rush — “there's no time to migrate, we'll sign and we'll reevaluate” — and others accept a gap: “Marketo ends on the first. We'll be dark for a couple of weeks.” One team that wants to move is waiting out its contract. Migrations that run long past the end date leave companies paying for two platforms at once.
Named in this context: Marketo · HubSpot · Klaviyo · Ometria
Small teams can only migrate one thing at a time
The people running the migration are usually also running the email program. “For bigger things, like an email replatform, our team was small; we could only really handle one of those at once,” one buyer says, and another describes doing it “in-house with my staff of two people on the email side.” Where the work depends on engineering or IT, buyers describe the migration waiting in someone else's queue.
Named in this context: Klaviyo · Epsilon · Salesforce Marketing Cloud
SMS can extend a broader cross-channel migration
When a company moves SMS alongside email, the two channels may have different launch dates. Buyers describe short-code applications and number registrations taking far longer than expected — one migration “took months and months and months because of a short code application” — and SMS still not launched after email went live: “We still haven't fully launched SMS.” Phased moves describe email landing in a few months and SMS months later.
Named in this context: Braze · Attentive · Zeta
Where do the ratings fit?
Implementation experience is one of several things behind each platform's rating. Braze and Salesforce Marketing Cloud draw the most implementation complaints here, largely because they are the most common destinations for larger migrations, while buyers moving to platforms built for smaller brands, such as Klaviyo, describe simpler set-ups. The ratings themselves, and what drives them, are on what ESP buyers wish they'd known.
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The counter-current: the migrations that went fast
The quick migrations here share a shape. Vendors ran the project plan and brought in the right specialists — one buyer describes a team “extremely helpful on the implementation side, the project management of that, bringing in the different SMEs as needed.” Smaller brands on simple, natively connected stacks describe set-ups that took weeks, and one chose its platform because “it was a lot easier to set up than those standalone systems.” And one company returning to a platform it had used before skipped the warming entirely, “because the IPs were already warm.”
What this means for your migration timeline
In these interviews the length of an email migration is set by the company's size and stack more than by the platform, and the slip comes from the data, the implementation team, warming, rebuilding flows, the contract calendar, the team's capacity and SMS. Our recommendations, not practices buyers describe: map every data feed the new platform needs before setting a date; ask who will run the project plan — the vendor or a partner — and how many people they will commit; confirm the new provider's sender-warming requirements early — whether the move needs dedicated-IP warming, a gradual volume ramp-up or another deliverability plan — and put that work in the schedule; budget for running both platforms until the core flows reach parity; start early enough that warming and parity work finish before peak season and before the old contract ends; and give SMS its own implementation timeline and launch milestone, separate from the email go-live date. To compare where buyers go when they switch, see why companies switch ESPs.
Common questions
How long does an ESP migration take?
Timelines generally rise with organizational complexity, and the ranges overlap. In these interviews small brands on straightforward stacks moving to platforms such as Klaviyo, HubSpot or Listrak describe a few weeks to about three months; mid-market moves to platforms such as Braze, MoEngage or Bluecore take about two to five months; and enterprise or multi-brand moves take six months to a year, with a few describing eighteen months or more. Among companies that gave both a plan and an outcome, none finished early.
Why do email platform migrations take longer than planned?
The recurring reasons in these interviews are connecting data and feeds to the new platform, implementation partners or vendor teams without the capacity the project needs, IP warming, rebuilding flows and journeys to reach parity with the old platform, contract dates that set the window, small internal teams, and SMS short codes and number registrations that can leave text messaging launching after email. Very few are about the software being hard to switch on.
How long does IP warming take when switching ESPs?
Buyers moving to new sending infrastructure who give a length describe about four to six weeks of gradually larger sends, and some describe sending from both platforms during that period. The requirement depends on the sending set-up rather than being fixed: one company returning to a platform it had used before skipped warming because its IPs were already warm. Several name warming as a reason they have not switched at all.
Does switching email platforms hurt deliverability?
None of the companies in these interviews reports an actual drop in deliverability after switching. Buyers treat warming as a cost and a risk to plan for — it adds weeks to the timeline and keeps some from moving — rather than as damage they experienced.
When is the best time to switch email platforms?
Buyers in these interviews time migrations around two things: when the current contract ends and when the busy season starts. Some will not start a migration going into the holidays, and one whose launch slipped into November and December describes how much that hurt. Leaving room for warming and parity work before peak season is our recommendation, not a practice buyers describe.
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