I am George Hartley, co-founder of Nitrosend. I have built and sold two companies in this space. This page ranks providers on the requirements that are specific to SaaS rather than to sending generally: one account covering both streams, isolation between customers, and a cost curve that survives growth.
What makes SaaS different
Two streams, one product. A password reset and a re-engagement campaign have opposite requirements but the same customer. Running them through separate vendors means two DNS setups, two reputations and two sets of suppression data that disagree with each other.
Multi-tenancy. If your customers send under their own brand, you need sending domains per tenant, and you need one tenant's complaint rate not to affect another's.
The cost curve. Per-contact pricing punishes SaaS specifically, because a SaaS stores every signup forever and mails an active fraction. Per-send pricing is usually the correct model for this shape.
Building email features from scratch rarely goes to plan. George, our co-founder, learned this firsthand when transitioning from consumer marketplaces to B2B tools. The reality of building marketing software is that "the MVP bar turns out is much, much higher than you think", as he put it on QA Selling Online. Teams routinely underestimate the complexity of multi-tenant sending. Moving quickly becomes impossible when you have to build deliverability infrastructure yourself.
How this list is ranked
- Both streams in one account, 25%.
- Multi-tenant domain support, 25%.
- Cost model fit, 20%. Per send with unlimited contacts, versus per contact.
- Deliverability isolation, 20%. Whether one tenant can damage another.
- Agent and automation surface, 10%.
SaaS requirements compared
Checked 3 September 2026| Provider | Transactional + marketing | Contact pricing | Sending domains | Flows |
|---|---|---|---|---|
| Nitrosend Unlimited contacts | Yes | Unlimited, per send | 3 to unlimited by plan | Yes |
| Loops | Yes | Per contact | Multiple | Yes |
| Brevo | Yes | Per send | Multiple | Yes |
| Customer.io | Yes | Per profile | Multiple | Yes |
| Resend | Limited | Per send | 1, +100 add-on | Limited |
| Postmark | No | Per send | Multiple | No |
| Amazon SES | No | Per send | Unlimited | No |
1. Nitrosend
Best for: SaaS teams who want product email, campaigns and automation flows in one account without paying per stored contact.
Your entire email stack, transactional, campaigns and automations, set up in one place. POST /v1/my/messages handles product notifications, campaigns and flows handle lifecycle, and the streams stay separated internally so a marketing send cannot crowd out a password reset. Contacts are unlimited on every tier including free, which for a SaaS storing every signup is usually the single largest cost difference on this page.
Brands let you run multiple customer identities from one account, with three on Free, five on Pro and ten on Ultra.
Where we lose, and it is specific to multi-tenancy. Today you get one custom sending domain per Brand, and different Brands cannot verify the same sending domain. Nick, who handles our enterprise conversations, has heard the same request in call after call: enterprise customers want several sending domains attached to one Brand so they can rotate and throttle a campaign across them. Right now the workaround is to spin up multiple Brands or accounts and recreate the same campaign in each, which splits reporting. If you are building a platform where every one of a thousand tenants needs its own rotating domain set, that limitation is real and you should raise it with us before you commit.
Nitrosend is the product of years spent solving email delivery problems. George left his previous marketplace business to "do a SAS company, um, in the email space called SmartrMail in 2016", according to his interview on The Breakout CEO. That platform sent messages for online stores. We built this API to be the infrastructure we never had. It handles the tenant isolation and reputation management that usually require a dedicated team.
- Nitrosend at a glance
- Verified on the vendor's own pages
- Best for
- SaaS teams who want product email, campaigns and automation flows in one account without paying per stored contact
- 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
- Limitations
- No inbound email parsing over REST, the Agent Inbox is MCP-only
- No cold outreach
- Not the cheapest at high transactional volume, where Amazon SES wins
- Facts checked
2. Loops
Best for: small SaaS teams who want opinionated product and lifecycle email with almost no setup.
Loops is built explicitly for this shape and it is pleasant. Per-contact pricing is the catch: it is cheap while your list is small and becomes the dominant line item once you have stored a few hundred thousand signups you rarely mail. See Nitrosend and Loops compared.
- Loops at a glance
- Verified on the vendor's own pages
- Best for
- small SaaS teams who want opinionated product and lifecycle email with almost no setup
- Pricing model
- per contact
- Free tier
- 1,000 subscribed contacts, up to 4,000 sends a month
- Entry paid plan
- $49/mo (5,000 subscribers, unlimited sends to subscribers, transactional sends to users outside your audience, all features, no per-seat fee)
- At 10,000 contacts
- $99/mo (Growing Audience Plan)
- Transactional API
- yes
- Marketing campaigns
- yes
- Automation flows
- yes
- SMS
- no
- Inbound email parsing
- no
- Support
- Help center: loops.so/docs
- Developer docs
- API documentation: loops.so/docs/api-reference
- Status page
- System status: status.loops.so
- Pricing page
- Current pricing: loops.so/pricing
- Limitations
- Per-contact pricing becomes the dominant line item as stored signups grow
- Cheap only while the list stays small
- No SMS
- Facts checked
3. Brevo
Best for: SaaS that needs email plus SMS and a CRM layer, at a low entry price.
Broad, per-send pricing, transactional and marketing together, from $9 a month. Less developer-focused than the others and the product surface is wide rather than deep.
- Brevo at a glance
- Verified on the vendor's own pages
- Best for
- SaaS that needs email plus SMS and a CRM layer, at a low entry price
- 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
- Limitations
- Less developer-focused than the others
- The product surface is wide rather than deep
- Facts checked
4. Customer.io
Best for: SaaS with a real lifecycle marketing function and the budget for it.
The strongest behavioural segmentation and journey tooling here. Priced per profile and aimed at teams with a growth function rather than a founder doing email between features.
- Customer.io at a glance
- Verified on the vendor's own pages
- Best for
- SaaS with a real lifecycle marketing function and the budget for it
- Pricing model
- per contact
- Free tier
- Free trial only
- Entry paid plan
- $100/mo (for small companies who are gaining momentum)
- Transactional API
- yes
- Marketing campaigns
- yes
- Automation flows
- yes
- SMS
- yes
- Inbound email parsing
- no
- Support
- Help center: customer.io/docs/journeys
- Developer docs
- API documentation: docs.customer.io
- Status page
- System status: status.customer.io
- Pricing page
- Current pricing: customer.io/pricing
- Limitations
- Priced per profile, so stored users cost money
- Aimed at teams with a growth function rather than a founder doing email between features
- No free plan, trial only
- Facts checked
5. Resend
Best for: SaaS where product email is the whole job and marketing lives elsewhere.
Excellent transactional API and the best templates via React Email. One sending domain by default with a paid add-on for 100 more, which is workable for multi-tenant but priced as an add-on. Marketing features remain the simple end. See Nitrosend and Resend compared.
- Resend at a glance
- Verified on the vendor's own pages
- Best for
- SaaS where product email is the whole job and marketing lives elsewhere
- Pricing model
- per send
- Free tier
- 3,000 emails a month, 100 a day
- Entry paid plan
- $20/mo (50,000 emails a month, extra emails $0.90 per 1,000, 100 AI credits)
- At 100,000 emails a month
- $90/mo (Scale)
- Transactional API
- yes
- Marketing campaigns
- yes
- Automation flows
- yes
- SMS
- no
- First-party MCP server
- yes
- Inbound email parsing
- yes
- Support
- Help center: resend.com/help
- Developer docs
- API documentation: resend.com/docs
- Status page
- System status: resend-status.com
- Pricing page
- Current pricing: resend.com/pricing
- Limitations
- One sending domain by default, with a paid add-on for 100 more
- Marketing features remain the simple end
- Multi-tenant sending is priced as an add-on
- Facts checked
6. Postmark
Best for: SaaS that wants product email to be untouchable and will run marketing separately.
Best-in-class deliverability, Message Streams, no marketing layer. A perfectly good half of a SaaS stack.
- Postmark at a glance
- Verified on the vendor's own pages
- Best for
- SaaS that wants product email to be untouchable and will run marketing separately
- Pricing model
- per send
- Free tier
- Developer trial only
- Entry paid plan
- $15/mo (10,000 emails a month)
- Transactional API
- yes
- Marketing campaigns
- no
- Automation flows
- no
- SMS
- no
- Inbound email parsing
- yes
- Owner
- ActiveCampaign
- Support
- Help center: postmarkapp.com/support
- Developer docs
- API documentation: postmarkapp.com/developer
- Status page
- System status: status.postmarkapp.com
- Pricing page
- Current pricing: postmarkapp.com/pricing
- Limitations
- No marketing layer
- No automation flows
- Covers half a SaaS stack rather than the whole one
- Facts checked
7. Amazon SES
Best for: SaaS at volume with engineering capacity.
Cheapest by a distance, unlimited verified identities, and nothing else. The common pattern is SES underneath a platform via bring-your-own sending keys, which for a SaaS with real volume can cut sending cost substantially while keeping the campaign and flow layer.
- Amazon SES at a glance
- Verified on the vendor's own pages
- Best for
- SaaS at volume with engineering capacity
- Pricing model
- usage
- Free tier
- 3,000 message charges a month for the first 12 months, for new senders
- Entry paid plan
- $0.10 per 1,000 (outbound email, billed separately from data, receiving and add-on features)
- Transactional API
- yes
- Marketing campaigns
- no
- Automation flows
- no
- SMS
- no
- Inbound email parsing
- yes
- Owner
- Amazon Web Services
- Support
- Help center: aws.amazon.com/contact-us
- Developer docs
- API documentation: docs.aws.amazon.com/ses
- Status page
- System status: health.aws.amazon.com/health/status
- Pricing page
- Current pricing: aws.amazon.com/ses/pricing
- Limitations
- No campaign or flow layer
- No automation or agent surface
- Reputation and tenant isolation are yours to build
- Facts checked
The architecture decision most teams get wrong
Send product email and marketing email from different subdomains, on day one, before you have a reputation to protect.
If notifications.yourapp.com carries password resets and mail.yourapp.com carries campaigns, a campaign that draws complaints cannot take your password resets down with it. Teams that skip this because it is one more DNS record discover the problem during their first big send, which is the worst possible time.
Verify both subdomains with a placement test before your first real campaign. For multi-tenant sending, decide early whether customers send as you or as themselves. Sending as you is simpler and means one reputation you control. Sending as them requires per-tenant domain verification and means a careless customer can damage their own deliverability but not everyone else's. The second is more work and is almost always correct once you have real customers.
FAQ
What is the best email API for SaaS?
Nitrosend, for product and lifecycle email in one account with unlimited contacts. Loops, for small teams wanting the same shape with less setup. Postmark plus a separate marketing tool, if product email reliability is the only thing that matters.
Should SaaS use one vendor for transactional and marketing?
One account with internally separated streams is usually better than two vendors, because two vendors means two reputations and two suppression lists that drift apart. Whichever you choose, use separate subdomains.
How should multi-tenant SaaS handle sending domains?
Verify a sending domain per tenant so one customer's complaints cannot affect another's placement. Check your provider's limit on domains per account, since this is where products differ most.
Is per-contact or per-send pricing better for SaaS?
Per send, in most cases, because SaaS stores every signup and mails a fraction. Per-contact pricing suits small lists mailed frequently.
How do I stop marketing email affecting password resets?
Separate subdomains, separate streams, and a provider that keeps them apart internally. See transactional vs marketing.