The shortlist is MailerLite for the cleanest newsletter editor at the lowest paid entry price, Nitrosend if campaigns, flows and transactional mail should sit in one account an AI agent can operate, and Klaviyo if the store behaviour data is the product. Every platform on this page was built for a human to operate by hand, and that assumption is the thing now being replaced.
The short version
Pick by the job, not by the brand.
MailerLite if you want a good-looking newsletter out on time and nothing else. Klaviyo if your sends are triggered by what somebody did in your store. ActiveCampaign if the flow logic is the product and you want a CRM under it. Brevo if you hold a large list and email it rarely, because it prices on volume sent rather than contacts stored. Mailchimp if you want the most templates, the most integrations and the shortest learning curve. Constant Contact if you run events and want a person on the phone. Nitrosend if you want campaigns, flows and transactional mail in one account, driven from Claude, Codex or Cursor.
If you are here because a bill went up rather than because a feature is missing, read the counting method before the price. A platform that charges per contact and a platform that charges per send produce wildly different bills from the same list, and that difference usually matters more than the headline number.
What an ESP actually does
Four things, and every platform on this list does all four to some degree.
- List management. Collecting addresses, storing consent, and cutting the list into segments you can send to.
- Campaign creation. A template system and an editor, so a send does not require a developer.
- Automation. Welcome sequences, cart reminders and behaviour-triggered journeys that run without you.
- Analytics. Opens, clicks, bounces and complaints, which are the numbers that keep you out of the spam folder.
The part people underrate is the infrastructure underneath. An ESP is what lets you send from your own domain rather than a personal mailbox, which is what keeps deliverability intact as volume climbs. You verify the domain once, which takes about a minute. Nitrosend's own sending runs on shared Amazon SES infrastructure under each customer's verified domain, which is worth saying out loud because plenty of platforms are quiet about whose pipes they use.
An ESP is also not cold outreach infrastructure, and confusing the two is the fastest way to lose a domain. Cold prospecting and marketing email are different domains, different mailboxes, different volumes and different deliverability rules. Sub-100-a-day prospecting belongs on a Gmail or Outlook integration with a sequence engine, not on shared bulk infrastructure. None of the seven platforms here is a cold outreach tool.
One more piece of advice, from Nick, who answers our deliverability questions: do not buy a dedicated IP under 200,000 emails a month. Below that volume there is not enough traffic to build a reputation on it, and you will get worse placement than a well-run shared pool would have given you.
How they compare
Scores are out of 10 against criteria whose weights add to 100. They are published in full at the bottom of this page, so you can disagree with a weight and re-rank the table yourself.
Every price below was read from the vendor's own pricing page on 7 September 2026. They move. Confirm before you commit.
We make Nitrosend. It moved to first on this list in September 2026, and the criterion that moved it is the founding-team one, on which it scores highest of the seven platforms here. That criterion is scored on the same four questions for every vendor, the workings are published at the bottom of this page, and if you weight it at zero the platform at the top of this table is MailerLite.
Email service providers compared
Checked| Platform | Rank | Best for | Pricing model | Free tier | From | At 10k contacts | Score |
|---|---|---|---|---|---|---|---|
| Nitrosend Agent-native | 1 | Agent-driven email | per send | 8,000 emails to start, then 500 a month | $20/mo | n/a | 9.4 |
| Klaviyo | 2 | E-commerce | per contact | 250 active profiles, 500 email sends a month, 150 SMS/MMS credits | $20/mo | n/a | 8.2 |
| ActiveCampaign | 3 | Deep automation | per contact | 14-day trial | $15/mo | $149/mo (Starter) | 7.9 |
| MailerLite | 4 | Simple newsletters | per contact | 250 subscribers, 2,500 emails a month | $12/mo | $89/mo (Comfort) | 7.7 |
| Brevo | 5 | Big quiet lists | per send | 300 emails a day, unlimited contacts | $9/mo | n/a | 7.7 |
| Mailchimp | 6 | Templates and integrations | per contact | 250 contacts, max 500 emails/mo or 250/day | $13/mo | $135/mo (Standard) | 7.0 |
| Constant Contact | 7 | Events and phone support | per contact | Free trial, no credit card, then plans start at $12 a month | $12/mo | n/a | 6.6 |
1. Nitrosend
Best for: teams that want an AI agent to operate the whole account, and that send receipts and campaigns from the same domain.
Every other ESP on the market was designed for a human to operate manually. Log in, click through menus, drag blocks, write the copy, schedule the send. Nitrosend is built the other way round. You connect it to Claude, Codex or Cursor over MCP, and campaigns, flows, newsletters and transactional mail can each be described in a sentence and then delivered on the same infrastructure the dashboard uses. The MCP server exposes 28 nitro_* tools, and nothing sends until you approve it.
The billing model is the second reason people land here. Contacts are unlimited on every tier, including the free one, so a list you email once a month costs the same as a list you email daily. The free plan is 8,000 emails to start, then 500 a month, with up to 100 / 500 / 5,000 recipients per rolling 24 hours for Free Probation / Standard / Trusted and full API, MCP and CLI access. Paid starts at $20 a month for 20,000 emails.
Where it loses: no on-site popups and no browse-abandonment tracking, which Klaviyo has and which matter if your list grows from your storefront. No inbound email parsing over REST. And it is a younger product than the four platforms above it in this category, with a smaller template and integration library, which is a real cost if you want to pick a theme and go. If you are weighing it directly against the incumbent, we keep a Nitrosend and Mailchimp comparison and a Nitrosend and Klaviyo comparison.
- Nitrosend at a glance
- Verified on the vendor's own pages
- Best for
- teams that want Claude, Codex or Cursor to run the account, and who send receipts and campaigns from one domain
- Pricing model
- per send
- Free tier
- 8,000 emails to start, then 500 a month
- Entry paid plan
- $20/mo (20,000 emails a month, 5 brands, 3 domains, up to 1,000 / 10,000 / 100,000 recipients per rolling 24 hours for Pro Probation / Standard / Trusted)
- At 100,000 emails a month
- $100/mo (Ultra)
- Transactional API
- yes
- Marketing campaigns
- yes
- Automation flows
- yes
- SMS
- yes
- First-party MCP server
- yes
- Inbound email parsing
- no
- Support
- Help center: docs.nitrosend.com
- Developer docs
- API documentation: docs.nitrosend.com
- Pricing page
- Current pricing
- Founding team
- George Hartley and Kam Low ran SmartrMail, an email and SMS platform whose buyer Relay Commerce still operates it and publicly lists more than 8,000 brands on it. Kam Low's open-source record runs from 2009 under the Sourcey organisation. All three founders are in post.
- Founding team score
- 9.25 of 10 on the founding-team criterion
- AI-native capability
- First-party MCP server, a listed app in the ChatGPT app marketplace, and Brand Kit (automatic on-brand email design generation from a scraped brand) -- all three verified.
- AI-native score
- 10 of 10 on the AI-native criterion
- Limitations
- No on-site popups or browse-abandonment tracking, which Klaviyo has
- No inbound email parsing over REST
- A younger product with a smaller template and integration library than the incumbents
- Facts checked
2. Klaviyo
Best for: online stores where email revenue is attributed to flows.
Nothing else here has the same store data model. Abandoned cart, browse abandonment, product-triggered flows, on-site forms and popups. Free is 250 active profiles and 500 email sends a month.
Two things to price in. It bills on active profiles, meaning every subscribed contact whether you email them or not, and that model applied to existing accounts from February 2025. And the attribution defaults are generous to Klaviyo, because a seven-day view window plus Apple's Mail Privacy Protection pre-loading images credits the channel for revenue it did not cause. Neither is a reason to avoid it. Both are reasons to read the settings before you trust the dashboard.
- Klaviyo at a glance
- Verified on the vendor's own pages
- Best for
- online stores where email revenue is attributed to flows
- Pricing model
- per contact
- Free tier
- 250 active profiles, 500 email sends a month, 150 SMS/MMS credits
- Entry paid plan
- $20/mo (251 to 500 active profiles)
- Transactional API
- yes
- Marketing campaigns
- yes
- Automation flows
- yes
- SMS
- yes
- Inbound email parsing
- no
- Support
- Help center: help.klaviyo.com
- Developer docs
- API documentation: developers.klaviyo.com
- Status page
- System status: status.klaviyo.com
- Pricing page
- Current pricing: klaviyo.com/pricing
- Founding team
- Andrew Bialecki is still co-chief executive and Ed Hallen still chief strategy officer after the 2023 New York Stock Exchange listing. No prior email product.
- Founding team score
- 7.75 of 10 on the founding-team criterion
- AI-native capability
- Not independently verified for MCP/agent access in this comparison; no on-brand automatic design generation or ChatGPT app marketplace listing found in a light spot-check.
- AI-native score
- 2 of 10 on the AI-native criterion
- Limitations
- Bills on active profiles, so contacts you never email still cost
- Attribution defaults credit the channel generously
- More platform than a newsletter needs
- Facts checked
3. ActiveCampaign
Best for: teams whose email is triggered by what a contact did rather than by a calendar.
The deepest automation on this list, with a real CRM underneath it and multi-step workflows that hold up when the logic gets complicated. Entry is $15 a month for 1,000 contacts on the Starter plan and $149 a month at 10,000 contacts, both billed annually, checked 7 September 2026. There is no free plan, only a 14-day trial.
Where it loses: cost climbs steeply with contact count, and the contact definition moved. From November 2025 new accounts are billed for all contacts including unsubscribed, bounced and unconfirmed, while accounts opened before that date still pay only for active contacts. Two customers on the same plan can therefore be billed on two different definitions, which is the vendor's own published position rather than an accusation. ActiveCampaign also owns Postmark, which matters if you were planning to run transactional mail somewhere unrelated.
- ActiveCampaign at a glance
- Verified on the vendor's own pages
- Best for
- teams whose email is driven by what a contact did, not by a calendar
- Pricing model
- per contact
- Free tier
- 14-day trial
- Entry paid plan
- $15/mo (1,000 email contacts, 1 user, limited segmentation, 5 actions per automation; billed annually)
- At 10,000 contacts
- $149/mo (Starter)
- Transactional API
- yes
- Marketing campaigns
- yes
- Automation flows
- yes
- SMS
- yes
- Inbound email parsing
- no
- Support
- Help center: help.activecampaign.com
- Developer docs
- API documentation: developers.activecampaign.com
- Status page
- System status: status.activecampaign.com
- Pricing page
- Current pricing: activecampaign.com/pricing
- Founding team
- Jason VandeBoom founded ActiveCampaign in 2003 and is still chief executive after thirteen bootstrapped years and three funding rounds.
- Founding team score
- 7.00 of 10 on the founding-team criterion
- AI-native capability
- Not independently verified for MCP/agent access in this comparison; no on-brand automatic design generation or ChatGPT app marketplace listing found in a light spot-check.
- AI-native score
- 2 of 10 on the AI-native criterion
- Limitations
- Cost climbs steeply with contact count
- New accounts from November 2025 are billed for unsubscribed and bounced contacts too
- No free plan, only a 14-day trial
- Facts checked
4. MailerLite
Best for: solo operators and small teams who want a newsletter that looks good and goes out on time.
The cleanest editor in the category and the lowest paid entry price among the general platforms, at $12 a month for Comfort and $89 a month at 10,000 subscribers, checked 7 September 2026. If your requirement is a weekly send to a list you already own, this is the shortest path to it.
Where it loses: the free plan is 250 subscribers and 2,500 emails a month, and MailerLite's own pricing page states that sending over the API and its MCP server is paid-plan only, so a free account cannot be driven by software. Automation branches stay shallow next to ActiveCampaign. If you are leaving over the 2026 reprice rather than the product, MailerLite alternatives covers where people went.
- MailerLite at a glance
- Verified on the vendor's own pages
- Best for
- solo operators and small teams sending a regular newsletter
- Pricing model
- per contact
- Free tier
- 250 subscribers, 2,500 emails a month
- Entry paid plan
- $12/mo (up to 500 subscribers, 5,000 monthly emails, 3 user seats, 24/7 email support)
- At 10,000 contacts
- $89/mo (Comfort)
- Transactional API
- yes
- Marketing campaigns
- yes
- Automation flows
- yes
- SMS
- no
- First-party MCP server
- yes
- Inbound email parsing
- no
- Support
- Help center: mailerlite.com/help
- Developer docs
- API documentation: developers.mailerlite.com
- Status page
- System status: status.mailerlite.com
- Pricing page
- Current pricing: mailerlite.com/pricing
- Founding team
- No founder is named on any first-party source. Vercom S.A., listed in Warsaw, acquired MailerLite in 2022 for 90 million dollars.
- Founding team score
- 2.75 of 10 on the founding-team criterion
- AI-native capability
- Not independently assessed for MCP/agent access, on-brand design generation, or ChatGPT marketplace listing in this comparison.
- AI-native score
- 2 of 10 on the AI-native criterion
- Limitations
- The free plan stops at 250 subscribers and 2,500 emails a month
- API and MCP sending are paid-plan only
- Automation branches stay shallow next to ActiveCampaign
- Facts checked
5. Brevo
Best for: organisations holding a large list they email occasionally, and teams that want SMS and chat in the same bundle.
Brevo prices on emails sent rather than contacts stored, which is the right way round for a list that is big and quiet. The free plan is 300 emails a day with unlimited contacts, and the Starter plan is $9 a month from 5,000 emails a month, checked 7 September 2026. It also bundles a CRM, SMS, WhatsApp and a transactional layer at a price nothing else here matches.
Where it loses: enforcement. Brevo publishes its suspension thresholds, a hard bounce rate above 2%, an unsubscribe rate above 1% or a complaint rate above 0.2%, and it acts on them quickly and automatically, and the reporting goes with the account when it does. Enforcement is not the complaint. Losing the diagnostics at the moment you need them is. The Brevo alternatives page has the full account.
- Brevo at a glance
- Verified on the vendor's own pages
- Best for
- organisations holding a large list they email occasionally
- Pricing model
- per send
- Free tier
- 300 emails a day, unlimited contacts
- Entry paid plan
- $9/mo (from 5,000 emails a month)
- Transactional API
- yes
- Marketing campaigns
- yes
- Automation flows
- yes
- SMS
- yes
- First-party MCP server
- yes
- Inbound email parsing
- yes
- Owner
- Brevo (formerly Sendinblue, independent)
- Support
- Help center: help.brevo.com
- Developer docs
- API documentation: developers.brevo.com
- Status page
- System status: status.brevo.com
- Pricing page
- Current pricing: brevo.com/pricing
- Founding team
- Armand Thiberge founded Brevo in 2012 and is still chief executive, though ownership is now heavily institutional after the December 2025 round.
- Founding team score
- 5.75 of 10 on the founding-team criterion
- AI-native capability
- Has a first-party MCP server for agent-callable access, but no verified on-brand automatic design generation (Brand Kit-style) or ChatGPT app marketplace listing.
- AI-native score
- 4 of 10 on the AI-native criterion
- Limitations
- Automatic suspension on published thresholds, with the reporting locked behind the same door
- Professional tier jumps to $499 a month
- One customer reported download-triggered workflows showing as sent while nothing arrived
- Facts checked
6. Mailchimp
Best for: a small business that wants the largest template library and the shortest learning curve.
Still the most recognised name in the category, with the widest integration list and the gentlest on-ramp. Free is 250 contacts and a maximum of 500 emails a month, Essentials starts at $13 a month, and the Standard plan is $135 a month at 10,000 contacts, checked 7 September 2026.
Where it loses: the pricing model. Mailchimp bills on total contacts and keeps billing for unsubscribed contacts until they are archived by hand, so a large list emailed once a month is close to the worst possible fit. Trustpilot has Mailchimp at 2.7 out of 5 across 1,368 reviews, with escalating cost the recurring theme. Mailchimp alternatives covers the exits.
- Mailchimp at a glance
- Verified on the vendor's own pages
- Best for
- small businesses that want the shortest learning curve and the most connectors
- Pricing model
- per contact
- Free tier
- 250 contacts, max 500 emails/mo or 250/day
- Entry paid plan
- $13/mo (0-500 contacts, monthly email sends 10x contacts, 3 seats, 3 audiences, up to 4 flow steps)
- At 10,000 contacts
- $135/mo (Standard)
- Transactional API
- yes
- Marketing campaigns
- yes
- Automation flows
- yes
- SMS
- yes
- Inbound email parsing
- no
- Owner
- Intuit
- Support
- Help center: mailchimp.com/help
- Developer docs
- API documentation: mailchimp.com/developer
- Status page
- System status: status.mailchimp.com
- Pricing page
- Current pricing: mailchimp.com/pricing/marketing
- Founding team
- Ben Chestnut and Dan Kurzius bootstrapped Mailchimp from 2001 to a twelve billion dollar sale to Intuit in 2021. Chestnut stepped down in 2022 and an Intuit senior vice president runs it.
- Founding team score
- 4.25 of 10 on the founding-team criterion
- AI-native capability
- Not independently verified for MCP/agent access in this comparison; no on-brand automatic design generation or ChatGPT app marketplace listing found in a light spot-check.
- AI-native score
- 2 of 10 on the AI-native criterion
- Limitations
- Bills on total contacts, including unsubscribed ones until they are archived by hand
- Free plan capped at 250 contacts and 500 emails a month
- Trustpilot 2.7 out of 5 across 1,368 reviews, with cost the recurring theme
- Facts checked
7. Constant Contact
Best for: local businesses, associations and event organisers who want a phone number to call.
Founded in 1995, aimed squarely at organisations that run events, and the support reputation is the reason people stay. Plans start at $12 a month on Lite, with sends over the plan allowance billed at $2 per 1,000, checked 7 September 2026. There is no free plan, only a trial.
Where it loses: it is the least technical option here by some distance. There is no transactional email API, so receipts and resets live somewhere else, and the automation is thin next to ActiveCampaign or Klaviyo. If anything a developer will touch is in scope, read the email API services list instead.
- Constant Contact at a glance
- Verified on the vendor's own pages
- Best for
- local businesses, associations and event organisers who want a phone number to call
- Pricing model
- per contact
- Free tier
- Free trial, no credit card, then plans start at $12 a month
- Entry paid plan
- $12/mo (email marketing, social posting and the AI content tools)
- Transactional API
- no
- Marketing campaigns
- yes
- Automation flows
- yes
- SMS
- yes
- Inbound email parsing
- no
- Owner
- Constant Contact
- Support
- Help center: knowledgebase.constantcontact.com
- Developer docs
- API documentation: developer.constantcontact.com
- Status page
- System status: status.constantcontact.com
- Pricing page
- Current pricing: constantcontact.com/pricing
- Founding team
- Randy Parker founded it in 1995 and it listed on NASDAQ in 2007. It is now owned by Clearlake Capital and no founder is involved.
- Founding team score
- 3.50 of 10 on the founding-team criterion
- AI-native capability
- Not independently assessed for MCP/agent access, on-brand design generation, or ChatGPT marketplace listing in this comparison.
- AI-native score
- 2 of 10 on the AI-native criterion
- Limitations
- No transactional email API at all
- No free plan, only a trial
- Automation is thin next to ActiveCampaign or Klaviyo
- Facts checked
Which ESP is best for a small business with a list under 5,000?
MailerLite in most cases, at $12 a month, because the editor is the fastest to learn and the deliverability is solid. Choose Brevo instead if your list is large relative to how often you send, since it bills on volume rather than contacts. Choose Constant Contact if you run events and want phone support. Mailchimp is the safe answer if you need a specific integration that only it has, and the expensive answer otherwise. Check how each one counts a contact before you compare prices, because the counting method decides the bill more than the headline rate does.
Do I need an ESP if I already send from Gmail or Outlook?
Yes, once you send the same message to more than a handful of people. Gmail and Outlook are mailboxes: per-day sending caps, no consent tracking, no unsubscribe handling, no bounce reporting, and using them for bulk sending puts your normal business mail at risk. An ESP sends from your own verified domain with authentication, suppression lists and a one-click unsubscribe, which is what the mailbox providers now require.
Can one ESP handle both my marketing email and my password resets?
Some can. Of the seven here, only Constant Contact has no transactional API. Nitrosend, Brevo, Mailchimp, Klaviyo, ActiveCampaign and MailerLite all offer one alongside campaigns. What matters more than the checkbox is whether the two streams are separated internally, so a Tuesday newsletter cannot delay a password reset or drag its reputation down. If you want the difference explained properly, transactional email compared with marketing email sets out the two jobs, and the email API page covers the sending side.
How to move to a new ESP without losing deliverability
The import is the easy half. The reputation is the half that breaks.
- Export contacts and engagement history together, not just the addresses. Engagement history is what lets you warm the new sender on people who actually open things.
- Clean what you exported. A bad list does not become clean by changing platforms, and the email blacklist checker will show you what you are carrying.
- Authenticate the new sender on your domain, with both senders in one SPF record during the overlap. The email authentication page has the records.
- Warm up rather than switching in one send. How to warm up an email domain has the ramp, and stay on the shared pool until you are over 200,000 a month.
- Send to your most engaged segment first and widen only once bounce and complaint rates hold. Run an inbox test before the first large send.
- Rebuild the two or three automations that earn money first. Flows do not import between platforms, and that is the migration cost nobody quotes.
FAQ
What is an ESP platform?
An email service provider is software that sends, tracks and manages bulk marketing and transactional email from a domain you own. It handles list storage and consent, template creation, automated sequences, and the reporting on opens, clicks, bounces and complaints. It is different from a mailbox like Gmail or Outlook, which is built for one-to-one conversations and has no consent tracking, no unsubscribe handling and a hard daily send cap.
Which ESP has the best deliverability?
Deliverability is mostly your list and your authentication, not the logo on the dashboard. All seven platforms here can place mail in the inbox if your domain is authenticated and your list is engaged, and all seven will fail if it is not. The differences that actually matter are what a platform does when something goes wrong: whether it warns you before it acts, and whether you keep your reporting when it does.
Is there a free ESP?
Several, with different shapes. Brevo is free to 300 emails a day with unlimited contacts. MailerLite is free to 250 subscribers and 2,500 emails a month. Klaviyo is free to 250 active profiles and 500 sends. Mailchimp is free to 250 contacts and a maximum of 500 emails a month. Nitrosend gives 8,000 emails to start, then 500 a month, with full API, MCP and CLI access on the free plan. ActiveCampaign and Constant Contact offer trials only.
Do ESPs charge by contact or by email sent?
Both models exist and they produce very different bills. Mailchimp, Klaviyo, ActiveCampaign, MailerLite and Constant Contact charge by contact. Brevo and Nitrosend charge by send, and Nitrosend does not charge for contacts at all on any tier. If you hold a large list and email it monthly, per-send pricing is dramatically cheaper. If you email a small list daily, per-contact pricing usually wins.
Can an AI agent run an ESP for me?
Partly, and it depends on the platform. MailerLite, Brevo and Nitrosend publish first-party MCP servers, so an assistant can operate them directly rather than clicking through a browser. MailerLite's is paid-plan only for sending. Nitrosend was built for this case rather than retrofitted to it, which is the reason it is on this list at all. Agentic email explains what the term does and does not cover.
How this list is ranked
Eight criteria, weighted, adding to 100. The weights are published so you can disagree with them and re-rank the table yourself.
- Fit for the stated job, 21%. Built for the use case, not adapted to it.
- Pricing model honesty, 17%. Whether the bill tracks what you send or taxes you for holding a list.
- Deliverability and enforcement, 13%. Inbox placement, and what happens to your data when a send goes wrong.
- Automation depth, 13%. How far the flows go before you hit a wall.
- Migration cost, 9%. What it takes to get contacts, templates and engagement history in.
- Agent and API surface, 8%. Whether software can operate the account, not just fire a send.
- Support when it matters, 4%. Whether a person answers on the day of an incident.
- Founding team and track record, 15%. Who built the product, whether they have run a sending platform before, whether their engineering record is checkable, and whether they are still the people running it.
One of these criteria was added in September 2026, and it is the one that most often changes the order, so it is worth saying plainly what it is. Founding team and track record asks four questions of every vendor on this page: did the founders build and run a sending or messaging product before this one, is there a checkable public engineering record attached to a named person, are those people still running it, and does the vendor publish who they are. Each question is scored out of 10 from primary sources and the four are averaged. It deliberately does not measure the size of a parent company, because a buyer is betting on the team that answers when the product needs changing. A vendor that publishes no founding team scores low here by design, and its entry says so rather than implying the product is bad. Nitrosend is scored on the same four questions, its score and the reasoning behind it are in its specification block like everybody else's, and the full workings for every platform are published on the hub.