ESP (Email Service Provider)

An Email Service Provider (ESP) is the software platform that handles email delivery infrastructure, subscriber management, campaign creation, automation sequences, and analytics. The ESP is the technical backbone of your newsletter: it manages the relationship between your sending domain and ISPs (Gmail, Yahoo, Outlook, Apple Mail), maintains your subscriber database, and processes the signals — bounces, complaints, opens, clicks — that determine your sender reputation. ESPs exist on a spectrum from enterprise marketing platforms to creator-focused newsletter tools. Legacy enterprise ESPs (Salesforce Marketing Cloud, HubSpot, Klaviyo) are built for complex multi-channel marketing operations with CRM integrations, advanced segmentation, and transactional email. Creator-focused ESPs (InfluencersKit, Beehiiv, Kit, Substack) are optimized for newsletter creation, subscriber growth, and monetisation — paid subscriptions, sponsorships, and programmatic ads — with a simpler interface and faster onboarding. The most consequential differences between ESPs for newsletter creators are: platform fees on paid subscriptions (Substack 10%, Beehiiv 2.9%, Kit 3.5%, InfluencersKit 0%), list portability (can you export all subscriber data including engagement history if you migrate?), sending infrastructure quality (shared IP versus dedicated IP, deliverability tooling), native monetisation features (does the platform handle programmatic ad placement or only subscriptions?), and automation depth (how complex can your welcome sequences, segmentation, and re-engagement campaigns be?). List portability deserves particular attention when choosing an ESP. Some platforms make export difficult or strip engagement data, meaning migrating to a new ESP requires re-warming your sender reputation from scratch with a cold list. Platforms that export full subscriber data with open and click history allow you to segment your list on import to a new platform, preserving the deliverability advantages of your engaged subscriber base. InfluencersKit exports full subscriber data in CSV and API format at any time. Deliverability infrastructure varies between ESPs in ways that aren't visible until something goes wrong. Shared IP sending pools, used by most free and low-tier ESP plans, mean your sender reputation is influenced by every other sender on that IP. One mass complaint from another sender on your shared IP can drop your inbox placement for 48–72 hours. Dedicated IPs — available on higher-tier plans — isolate your reputation to your own sending behavior, but require warmup: gradually increasing send volume over 4–6 weeks before sending your full list, so ISPs can build a reputation profile for the new IP. Shared IPs are fine for most creator newsletters; dedicated IPs matter primarily when you're sending 100,000+ emails per month and want complete control over the IP's sender history.