What is an ESP (Email Service Provider)?
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If you've ever used Mailchimp, Klaviyo, or Postmark to send email, you've already used an ESP. You just might not have known the name for it.
An Email Service Provider (ESP) is a company that gives you the infrastructure, software, and tools to send email at scale. Instead of running your own mail servers, managing IP addresses, and handling bounce processing yourself, you plug into an ESP and they deal with the technical plumbing.
ESPs generally fall into a few categories based on what kind of email they're built for:
- Marketing ESPs handle newsletters, campaigns, and promotional sends. Examples: Mailchimp, Klaviyo, Brevo (formerly Sendinblue), ActiveCampaign, MailerLite.
- Transactional ESPs handle triggered, one-to-one emails like receipts, password resets, and shipping notifications. Examples: Postmark, Twilio SendGrid, Mailgun, Amazon SES.
- All-in-one platforms combine marketing automation, CRM, and email in one place. Examples: HubSpot, Salesforce Marketing Cloud, Braze.
What an ESP actually handles for you goes beyond just hitting send. You're getting managed sending infrastructure (IP addresses, DNS config, mail servers), bounce and complaint processing, unsubscribe management, suppression lists, and analytics like open rates and click tracking. That's a lot of moving parts you don't have to build yourself.
The most important decision when picking an ESP is whether you need marketing email, transactional email, or both. Some platforms handle both, but keep a close eye on whether they separate your sending streams. If your welcome campaign triggers complaints and your password reset emails share the same IP, those resets can start landing in spam too. That's a bad day.
Pricing models also vary quite a bit. Some charge per contact stored (Mailchimp, Klaviyo). Some charge per email sent (Brevo, Amazon SES). Some charge by feature tier (HubSpot, ActiveCampaign). The right model depends on your list size and how often you send.
And a few worth knowing beyond the big names: Customer.io and Iterable are built for behavioral messaging in SaaS products. Elastic Email and SMTP2GO are affordable options for smaller senders. And Postmark is unique in that it refuses to send marketing email at all, only transactional, which keeps its sending reputation very clean.
Not sure which ESP fits your setup? Our SOS hotline is free and we'll walk through what actually matters for your situation (no pitch, promise).
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