A quick reference to support marketers and technical teams during an ESP migration.
🔄 General Migration Strategy
Q: How long does a typical ESP migration take?
A: Migrations usually take 2 to 12 weeks. This is such wide time range because it depends on:
- Dedicated or Shared IP. The numbers below refer to Shared IPs and should be doubled for Dedicated IPs. See our guide: How to decide between dedicated and shared IPs
- Data volume. Rough Guide: 0-100k → 1-2 weeks. 100k-1M → 4 weeks. 1M+ → 4-6 weeks.
- List quality. Active data sends better. Invalid data and typos can lead to long-term blocks. Leaving re-engagement campaigns until after migration simplifies and speeds migration
- Sending strategy and frequency.
- Technical and organisational limitation, requirements and constraints setup.
Q: What causes migration and warm-up to fail or be delayed?
A: Data quality issue, low recipient engagement, rushing volume increases. Bad data in the first weeks can cause months of issues. First impressions count - so issues while establishing a reputation can have a lasting, damaging effect.
Even with small lists, you should allow 1-2 weeks, starting with the best data, increasing volumes each time you send. Avoid volume spikes, leave inactive data until last, and ensure currently-suppressed data stays off your new list
Q: Can I “lift and shift” everything in one go? Can I keep my existing Sender Domain?
A: Not easily. A successful migration typically requires a phased transition, running old and new platforms in parallel for the period that you are implementing, testing and warming up.
Q: When is the migration officially complete?
A: You define this upfront. Agree internally what constitutes “migration complete”, and when the old platform can be decommissioned.
- are re-engagement campaigns part of migration, or for after a successful migration?
See: How should I segment my data for warm-up - What automations and campaigns are included in your migration MVP, and which come later?
- For how long do images, links, replies, bounces and unsubscribes need to continue working in your old platform?
- When will you extract all historic engagement and suppression data?
Stakeholder alignment is critical.
🧠 Data & Audience Strategy
Q: Should I migrate all my email data, even inactive contacts? What about invalid and suppressed contact data?
A: Contact data should only imported into a new platform if you have a strategic reason.
- Inactive contact data will likely contain both valuable customer data and "dead" data which should be deleted. MIgrate inactive customer data for re-engagement. Delete old, inactive contact data with no value.
- Invalid (bounced) and suppressed email contacts data may still be valid and active in other channels. Migrate only that which may be used for other channels, but do not subscribe invalid email addresses to your email contact lists
Q: How should I segment my data for warm-up?
A: Break your audience into segments based on how likely they are to engage:
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0–90 day active (clicked link, visited website/app)
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90–365 day active (clicked link, visited website/app)
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Long-term inactive customers (no activity in last year, but with previous purchase)
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Long-term inactive non-customers (no activity in last year, and no previous purchase)
You are recommended to exclude Segment 4 - Long-term inactive non-customer data, from the migration process. Any review and final testing of this low-value, high-risk data should come after migration is complete. See When is the migration officially complete?
[Data Segmentation for Warm-Up Success (coming soon)] for more.
Q: How do I manage contact lists in both old and new platform
A: When creating segments to import into the new platform, create a new unique ID for every contact based on last engagement/purchase date. Ensure that ID is identical in both old and new platform.
When you want to send to your top 15k active contacts in your new platform you simply:
- New platform warm-up segment: include ID between 1 and 15000
- Old platform: exclude ID between 1 and 15000
This means you can easily coordinate inclusion and exclusion lists between platforms based on your warm-up lists, using engagement and purchase dates
📈 IP and Domain Warm-Up
Q: Do I need a new IP address or can I use a shared one?
A: It depends on your volume, any business needs, your marketing and service message requirements. Dedicated IPs offer control but require warming up from zero, and should be seen as the expert solution. Shared IPs offer speed, capacity, simplicity and significantly easier onboarding; but less control. See Choosing Between Dedicated and Shared IPs.
Q: How fast can I warm up my domain and IP?
A: Migrations usually take 2 to 12 weeks. This is such wide time range because it depends on:
- Dedicated or Shared IP. The numbers below refer to Shared IPs and should be doubled for Dedicated IPs. See our guides: How to decide between dedicated and shared IPs and Warm-up IPs at SAP Emarsys
- Data volume. Rough Guide: 0-100k → 1-2 weeks. 100k-1M → 4 weeks. 1M+ → 4-6 weeks.
- List quality. Active data sends better. Invalid data and typos can lead to long-term blocks. Leaving re-engagement campaigns until after migration simplifies and speeds migration
- Sending strategy and frequency.
- Technical and organisational limitation, requirements and constraints setup.
Q: I'm using shared IPs, do I need to warm-up?
A: Yes. Your sender domain needs to establish a trusted reputation.
See our guide: Warm-up IPs at SAP Emarsys
Q: I have a small list, do I need to warm-up?
A: Yes. Senders with smaller lists still need to establish a reputation. But also, those with smaller lists may be tempted to just start sending to "everything" and not segment properly. Long-term inactive data should not be used for the first two weeks while your new domain reputation is established.
Q: Is there a tool or calculator to help plan ramp-up volume?
A: A custom ramp-up calculator helps plan daily send limits based on data quality and available warm-up time. Coming soon: [How to Create a Ramp-Up Calculator]
⚙️ Technical Setup, Sender Domain & DNS
Q: Can I create a new Sender Domain for my new platform?
A: Yes. This should be a new subdomain of your ecommerce or corporate domain
Q: What is a Cousin Domain, and how is this different to a sub-domain?
A: A cousin domain is a domain name that resembles your real domain, with misspellings, substitutions, or added characters. These are flagged as spam, phishing or suspicious and should not be used for email sending. Only subdomains should be used for email.
In terms of email, if your real domain was www.example.com:
- exampleemails.com would be classed as a cousin domain - this would not be trusted, as any malicious sender could purchase and configure for use, pretending to be you
- email.example.com is a sub-domain of your existing domain - this will be trusted, as only your organisation can create this
Q: Can I use the same Sender Domain from both platforms at once?
A: Not recommended, as email settings will be confused, pointing in two directions to both old and new platforms. Instead, create a new subdomain, which will inherit the trust of your existing domain.
Q: Do I need different subdomains for marketing and service messages?
A: This is recommended to ensure service message delivery optimisation, and to allow mailbox providers to deliver updates and notifications to the correct email folder
Q: Do I need different subdomains for marketing and service messages?
A: It can help message queueing and folder placement, as with sender domains. If using shared IPs, your service provider may be able to provide both marketing and service message shared IPs/Pools. If using dedicated IPs, a dedicated IP for service messages (distinct from marketing IPs) is only recommended if service volumes are large enough to establish and maintain a reputation. There is no defined figure for this, but certainly less than 10k service emails per day would not warrant a dedicated IP. Instead, with dedicated IPs you can put service messages with your marketing dedicated IP or, if available, put service messages on your provider's shared Service Message IPs
Q: What DNS changes are required?
A: Your new provider will provide the DNS settings to use
For SAP Emarsys see: Domain Validation
📤 Campaign Strategy During Migration
Q: How can I speed up my warm-up?
A: Send to your most active contacts first (e.g. 0-90 day clickers), and increase volume every day. You can speed things up by sending 2–3 times daily in the first 1-2 weeks, but only to your most engaged users. Use content designed to generate engagement and clicks. Monitor both positive and negative metrics, and adjust your plan (speed up or down) based on results. Also remember that warm-up is a process, not a race. Read more tips to speed up migration.
Q: Do I need to inform my customers and subscribers?
A: This would be recommended if you are making visual or wording changes. Just changing to a new sub-domain would not warrant an alert. See more in our rebranding guide
Q: Should I change my content or sending strategy changes during migration?
A: Avoid major changes. However, in the first two weeks you want to generate positive engagement from your recipients, so consider using your best offers for warm-up emails.
Q: Should I use service messages to generate engagement during warm-up?
A: While service messages do generate high engagement, it's recommended to stick with marketing messages for the first 1-2 weeks while you establish a base reputation and the technology is tested. A batch marketing message which fails can be resent the next day with little impact; whereas a service message lost or delayed for a day could have a significant impact to your customer.
Q: What if my deliverability drops during warm-up?
A: Pause, assess, and adjust. Don’t plough on. Common causes include bad list quality, sending too fast, or mixing low-engagement contacts too early. See [Email Warm-Up Recovery Steps (coming soon)].
Q: Why are my open rates low?
A: Sending from a new sub-domain will reset image "pre-fetching". Use click rates to review campaign performance. Read more here: Open rates in email marketing