Seedlist Warmup is E-Warmup’s solution for improving email deliverability when you cannot connect a mailbox via SMTP or traditional inbox sync.
Many modern marketing platforms (ESPs) do not allow you to connect individual mailboxes the same way Gmail or Outlook does. In these cases, classic AI mailbox warmup is not possible. Seedlist Warmup solves this by giving you access to curated lists of real, engaged seed inboxes across major providers (Gmail, Outlook, Yahoo, and more).
You simply download the seed list, import it into your ESP as a campaign audience, and send to it. Our seeds open, read, click, recover emails from spam, and mark messages as important — generating authentic engagement signals that train spam filters and improve your sender reputation, domain, and IP health.
Standard email warmup works by connecting your mailbox to a warmup tool over SMTP and IMAP. The tool sends messages from your address, and a network of real inboxes opens, replies, and marks them as important. Those engagement signals teach Gmail, Outlook, and other mailbox providers that mail from your domain is wanted.
That model breaks down the moment your sending happens somewhere that doesn't hand out SMTP credentials.
Most email marketing platforms, CRMs, and ecommerce messaging tools are closed systems. They send on your behalf from their own infrastructure. There's no mailbox for a warmup tool to log into, no IMAP folder to read replies from, and often no way to route an individual message through an external connection. If you run your campaigns in Klaviyo or Mailchimp, a conventional warmup tool has nothing to connect to.
The reputation problem doesn't go away, though. Your domain still needs engagement signals. A new sending domain, a fresh dedicated IP, or a list that's gone quiet for months will land in Promotions or Spam regardless of which platform you send from.
Seed list warmup closes that gap.
Seed list warmup works with any platform you can upload a contact list to. That's the only requirement. You do not need SMTP access, IMAP access, or an API integration.
It is designed for any team sending from non-SMTP or marketing-platform environments.
Customers commonly use E-Warmup seed lists with:
Ecommerce and retail marketing Klaviyo · Omnisend · Attentive · Sendlane · Drip · Listrak · Ometria · Bloomreach Engagement · Postscript · Yotpo Email · Privy · Shopify Email · BigCommerce · WooCommerce email
General email marketing Mailchimp · Constant Contact · AWeber · GetResponse · Campaign Monitor · MailerLite · Moosend · Benchmark Email · EmailOctopus · Zoho Campaigns · Sender · Flodesk · Mailmodo · EngageKit · Ortto (formerly Autopilot) · Emma (Marigold)
Creator and newsletter platforms Kit (formerly ConvertKit) · beehiiv · Substack · Ghost · Buttondown · Curated · Kajabi · Podia · Teachable · Thinkific
CRM and marketing automation HubSpot · ActiveCampaign · Salesforce Marketing Cloud · Marketo Engage · Salesforce Account Engagement (Pardot) · Oracle Eloqua · Adobe Campaign · Braze · Iterable · Customer.io · Blueshift · Cordial · Emarsys · Dotdigital · Insider · MoEngage · CleverTap
Support and product messaging Intercom · Zendesk · Front · Help Scout · Freshdesk
Website builders and commerce platforms Squarespace Email Campaigns · Wix Email Marketing · Webflow · Kartra · Systeme.io
Don't see yours? If you can import a CSV of contacts into it, seed list warmup will work.
Ecommerce and DTC brands. If your flows and campaigns run through Klaviyo, Omnisend, or Attentive and your emails are landing in Promotions instead of Primary, seed list warmup builds the engagement history that moves them.
Newsletter operators and creators. New Substack, beehiiv, or Kit publications start with no sending history at all. Warming the domain before your first real send protects your open rates from day one.
Teams on a closed CRM. HubSpot, Marketo, and Salesforce Marketing Cloud handle sending internally. Seed lists are the only way to warm those sends.
Anyone launching a new domain or IP. A fresh domain has no reputation. A dedicated IP has none either. Seed list warmup builds it before real subscribers ever see a message.
Anyone recovering from a deliverability drop. After a spam-trap hit, a blacklist entry, or a period of low engagement, rebuilding requires consistent positive signals. Seed lists supply them on any platform.
Seed list warmup is sold as credits rather than a monthly subscription.
One credit equals one seed contact. Sending to a 200-address seed list uses 200 credits.
Credits never expire. Buy them once and use them across campaigns whenever you need them.
Credits are separate from your mailbox plan. You can buy seed credits on any plan, including Free Forever, and they don't count against your connected-mailbox limits.
You choose the list size. Smaller lists cost less and give a narrower placement read; larger lists give more reliable provider-level data.
Current credit pack pricing is on the E-Warmup Dashboard.
These get confused, and they aren't the same thing.
Inbox placement testing is a diagnostic. You send one campaign to a seed list and get a report showing where it landed. It tells you the state of your reputation right now. It doesn't change anything.
Seed list warmup is a treatment. The seed inboxes actively engage — opening, reading, replying, rescuing from Spam — over a sustained period, which is what teaches mailbox providers to trust you.
E-Warmup's seed lists do both. Every send reports placement, and every send builds reputation.
Seed-list Warmup
No SMTP? Warm up anyway
Does seed list warmup work if my platform has no SMTP access?
Yes. That's exactly what it's built for. You only need the ability to import contacts and send to them.
Will seed emails hurt my open rates or engagement metrics?
Seed addresses engage with your mail, so they register as active subscribers inside your platform. Keep them in a dedicated segment so you can exclude them when reporting on real campaign performance.
How long does seed list warmup take to work?
Most senders see placement improve within two to three weeks of consistent sending. A badly damaged domain takes longer. A brand-new one usually moves faster.
Can I use seed list warmup and mailbox warmup together?
Yes, and many customers do. Warm your connected mailboxes for cold outreach while warming your marketing platform with seed lists. They're independent and they reinforce each other.
Do credits expire?
No. Credits stay in your account until you use them.
How many seed addresses should I send to?
Start with a smaller pack to establish a baseline, then scale up. Larger lists give more statistically reliable per-provider placement data.
Can I see which providers my emails landed in?
Yes. Placement is broken out by mailbox provider, so you can tell whether Gmail and Outlook are filtering you differently.
