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Glossary · E

What an email service provider does, and how to choose one for a shop

The software that holds your list and sends your email. For a shop, the useful question isn't which one is best. It's what each one knows about your customers.

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040ESP (Email Service Provider)
A company that offers email marketing or bulk email services, like Klaviyo, Mailchimp, or Sendlane.
A growth overview inside a live client Klaviyo account, attributed revenue split between campaigns and flows month by month
Examples
Klaviyo, Mailchimp, Omnisend, Shopify Email and Sendlane
Usually billed on
The size of your list
Decides
What you can segment on, which flows you can build, what you can prove
Our interest
Official Klaviyo partners, and we say so up front

What an email service provider does behind the send button

Writing the email is the visible part. The ESP does the jobs nobody sees, and most of them are about staying out of the spam folder.

  • Holds your contacts, and the consent each one gave
  • Sends at volume from servers mailbox providers recognise
  • Signs your mail with your domain, so Gmail can tell it's really you
  • Processes bounces, unsubscribes and spam complaints, and stops mailing those people
  • Triggers flows, sends campaigns and reports what each one earned

The signing isn't optional any more. Google's sender guidelines ask bulk senders to authenticate with SPF, DKIM and DMARC, the records that prove mail really comes from you, and to offer one-click unsubscribe. A decent ESP walks you through the setup.

Marketing platforms and transactional senders do different jobs

Marketing ESPs, like Klaviyo or Mailchimp, send campaigns and flows to people who agreed to hear from you. Transactional services, like Postmark or Amazon SES, send receipts and password resets for developers' apps. A Shopify shop rarely needs the second kind.

That's because Shopify sends order confirmations and shipping updates itself. You can move those into Klaviyo to match the rest of your email, once each message is approved as transactional. Either way, only one system should send each one.

Choosing an email service provider on what it knows

AskBecause it decides
What does it store from the shop?Which flows you can build at all
Can one flow treat different customers differently?How personal the mail gets without copies everywhere
Can it show email revenue next to the shop's total?Whether anyone upstairs believes the number
Who else knows how to use it?Who you can hire, and how fast
What does leaving cost?Flows and engagement history rarely travel

We're official Klaviyo partners, so you know which way we lean. For a shop with real repeat purchase and several product lines, we'd pick Klaviyo. For a small list and a monthly newsletter, Mailchimp, Omnisend or Shopify Email will send it perfectly well.

Weighing a move? Read what breaks in a Mailchimp to Klaviyo migration first. Most of it breaks in either direction.

Glossary · related

Related terms

KlaviyoThe leading email marketing platform designed for ecommerce businesses, offering advanced segmentation and automation.Email deliverabilityThe ability of an email to reach the recipient's inbox without being blocked or filtered as spam.IP warmingGradually increasing email send volumes to establish a good sender reputation with ISPs when using a new IP address.DKIMAn email authentication method that allows the receiver to verify that an email was sent and authorised by the owner of the domain.Transactional emailsEmails triggered by specific user actions, such as order confirmations, shipping notifications, and password resets, essential for customer communication.IntegrationsThe process of linking together different computing systems and software applications physically or functionally, to act as a coordinated whole.
How we build email systemsWhat we do inside Klaviyo
FAQs

FAQs

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Is Shopify Email an email service provider?

Yes, a simple one. It sends campaigns and basic automations to your Shopify customers from inside your admin, and for a monthly newsletter that's enough. You'd add a dedicated ESP when you want flows that react to what people do, segments built on behaviour, and reporting you can take to a board.

Does changing ESP affect deliverability?

For a while, yes. Your mail starts coming from new servers, so mailbox providers need to see good engagement before they trust your usual volume. Authenticate the domain on the new platform first, start with your most engaged subscribers, and build up over a few weeks before you mail the whole list.

What is the difference between an ESP and a CRM?

A CRM keeps the record of your relationship with each customer, usually for sales or service teams. An ESP sends the email. Klaviyo blurs the line, because it holds the customer data your flows run on, so plenty of shops treat it as their customer database too.

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