Postmark Alternative
When message streams
aren't enough
Postmark is one of the best email services out there. Excellent deliverability, clean API, genuine care for the craft. But if you're building a platform where your customers send email through you, message streams top out, there's no automated domain onboarding, and the transactional-only policy becomes a wall. Ark was built for exactly this.
Acme Corp
3 domains
StartupXYZ
1 domain
Agency Pro
5 domains
ShopFront
2 domains
Every tenant gets isolated domains, credentials, analytics, and suppression lists
Why platform teams look for Postmark alternatives
Postmark was founded in 2010 by Wildbit with a clear philosophy: transactional email should be fast, reliable, and treated differently from bulk mail. They built an excellent reputation through strict sender vetting and a genuine commitment to deliverability. For single-sender transactional email, Postmark remains one of the best options available.
The challenge begins when you're not a single sender. If you run a SaaS platform where your customers send email through you, Postmark's model starts to strain. Message streams are how Postmark organizes email within a server: up to 10 per server on the free and basic tiers, 30 on Pro, and unlimited on the Platform plan at $18/month. They're a workaround for multi-tenant isolation, not a solution for it.
At 50 or more customers, the model breaks down. You're juggling servers, streams, and manual domain provisioning. Each customer's domain needs manual DNS setup. There's no automated onboarding flow you can hand to your users. And the transactional-only policy means if any of your customers need to send marketing email, you need a second provider entirely.
Ark is the alternative. Multi-tenancy isn't a bolt-on here. It's the entire architecture.
Multi-tenant architecture
Postmark organizes email through a Server and Streams hierarchy. Each server contains message streams, which can be either transactional or broadcast. The free tier allows up to 10 streams per server. Pro gives you 30. The Platform plan removes the limit but starts at $18/month before any sending costs.
For multi-tenant platforms, this model forces awkward tradeoffs. Do you create one server per customer and manage dozens of API tokens? Or share a server and try to separate customers using streams, losing isolation in the process? Neither option scales cleanly, and both require significant custom engineering.
Ark takes a fundamentally different approach. The entire system is organized as a white label email API hierarchy: Platform, Tenants, Domains, and Email. When you create a tenant in Ark, everything is scoped to that tenant — their domains, credentials, webhooks, suppression lists, and analytics. There's no artificial limit on tenant count beyond what your plan allows for domains.
Postmark approach
10 streams/server (free) · 30 (Pro) · Transactional or broadcast only
Ark approach
Tenant A
Tenant B
Tenant C
No tenant limit · Isolated by default · All plans
Postmark message streams
- 10 streams per server (free/basic)
- Server-level API tokens, not tenant-level
- Transactional vs broadcast classification required
- Multi-tenant requires custom server management
Ark tenants
- Available on all plans (from $29/mo)
- Per-tenant credentials, scoped API access
- No email type restrictions per tenant
- Built for platforms with external customers
Domain management and onboarding
Postmark provides the DNS records you need for domain authentication. You get DKIM and return-path records through the dashboard or API, and the documentation is clear. But the process stops there. Your customer gets a set of DNS records and has to figure out how to add them to whatever provider they use.
Domain limits also vary by plan. Postmark's free tier allows 10 custom sending domains. The Basic plan limits you to 5, Pro gives 10, and the Platform plan provides unlimited domains. If you're onboarding dozens of customers each with their own domain, you're quickly looking at the Platform tier.
Ark provides guided domain onboarding. When a tenant adds a domain, Ark detects their DNS provider and shows them the exact steps for their specific provider. There are dedicated setup guides for Cloudflare, Vercel, Namecheap, Porkbun, GoDaddy, DigitalOcean, Netlify, and more. After verification, a DomainDNSError webhook fires if records become invalid later.
Our guide to sending email from your customer's domain covers the full DNS and reputation isolation architecture.
Sending domain
We'll show Cloudflare-specific DNS instructions
Required DNS records
TXTSPF VerifiedCNAMEDKIM VerifiedCNAMEReturn PathPending[email protected]Hard bounceEach tenant's suppression list is independent — Acme's bounces don't affect StartupXYZ
Hard bounce
Instant suppression
Spam complaint
Instant suppression
Soft bounce
18 retries over 48h
Deliverability and reputation isolation
Postmark has excellent deliverability. Genuinely. Fifteen years of strict sender vetting, careful IP management, and a transactional-only policy have given them one of the strongest reputations in the industry. If you're sending your own transactional email, Postmark's deliverability is hard to beat.
The difference matters for multi-tenant platforms. Postmark's message streams share server-level sending reputation. If one customer in your server sends poorly, it can affect streams in the same server. Postmark protects against this through content restrictions — the transactional-only policy is itself a deliverability strategy.
Ark takes a different approach: reputation isolation per tenant. Every tenant sends from their own authenticated domains with independent suppression lists. Rather than restricting content types, Ark isolates reputation so that one tenant's behavior cannot impact another. Hard bounces trigger immediate per-tenant suppression. Spam complaints are handled at the tenant level.
On the Scale plan, tenants can get dedicated IPs for full IP reputation control. But for most platforms, per-tenant domain isolation and automatic suppression management is what keeps deliverability healthy.
Pricing comparison
Postmark's Platform plan starts at $18/month for 10K emails plus $1.20 per additional 1K. Here's how it compares at different volumes.
Monthly volume
Postmark Platform
Ark
10,000
emails
$18/mo
$29/mo
includes 50K
50,000
emails
~$66/mo
$29/mo
included
100,000
emails
~$126/mo
$29/mo + overage
250,000
emails
~$306/mo
$99/mo
Growth plan
1,000,000
emails
~$1,206/mo
$499/mo + overage
Scale plan
Postmark Platform
Required for multi-tenant
- Unlimited message streams
- Excellent deliverability reputation
- Transactional email only policy
- $1.20 per 1K emails overage
- Guided DNS onboarding
- Per-tenant analytics
- Two-level webhooks
- Marketing email support
Ark Starter
Full multi-tenant features
- Unlimited tenants
- Up to 10 domains
- Per-tenant isolation on all plans
- 50K emails/month included
- Guided DNS onboarding
- Per-tenant analytics
- Two-level webhooks
- No email type restrictions
As you scale, Ark's Growth plan ($99/month) supports 100 domains and 250K emails. The Scale plan ($499/month) supports 1,000 domains and 2M emails with dedicated IP options.
$ curl -X POST \
https://api.arkhq.io/v1/tenants/{id}/messages
{
"to": "[email protected]",
"from": "[email protected]",
"subject": "Order confirmed",
"html": "<h1>Thanks!</h1>"
}
# 200 OK — message queued
/emails/emails/batch/tenants/{id}/domains/tenants/{id}/suppressions/tenants/{id}/webhooks/tenants/{id}/credentials/tenants/{id}/usage/platform/webhooksDeveloper experience
Postmark has excellent developer experience. Their API is clean, well-documented, and consistent. Official SDKs cover Rails, .NET, Java, PHP, and Node.js, with community libraries for many other languages. The developer documentation is genuinely among the best in the email industry.
Where the two diverge is in multi-tenant operations. Postmark's API is organized around servers and message streams. Managing multiple customers means managing multiple server tokens and coordinating across them. There's no unified API surface for multi-tenant workflows.
Ark's API is tenant-scoped by design. There are 66 endpoints covering the full lifecycle: tenants, domains, credentials, messages, webhooks, suppressions, usage tracking, and logs. Official SDKs are available for Python, Node.js, Ruby, and Go — all with full type definitions.
Ark also ships with SMTP support for platforms that need it. Self-hosted tools like Listmonk, Coolify, or Metabase can send through Ark by changing one SMTP configuration.
26 MCP tools for AI assistants. Manage email infrastructure using natural language.
Per-customer analytics and debugging
When a customer asks "why didn't my email get delivered?", you need to answer fast. Postmark's activity feed shows message-level data, but it's scoped to the server level, not per customer.
Ark provides per-tenant message logs, delivery status tracking, and bounce analysis out of the box. Every message sent by a tenant is queryable through the API with full delivery details.
Webhooks are where Ark really differentiates for platforms. You get two levels: tenant-level webhooks that fire for a specific tenant's events, and platform-level webhooks that fire for all tenants with a tenant_id field in the payload.
{ "event": "delivered",
"tenant_id": "ten_abc123",
"message_id": "msg_xyz",
"recipient": "alice@..." }
Server
Postmark webhooks (per server)
∞
Ark webhooks (per-tenant + platform)
Email type flexibility
Postmark has a transactional-only policy. This is intentional and, for their use case, smart. By restricting what goes through their servers, they maintain exceptionally clean IP reputation. Broadcast streams exist, but they're carefully vetted and still subject to strict content policies.
For platforms, this creates a real problem. Your customers don't always draw a clean line between transactional and marketing email. A SaaS product might need to send password resets, usage notifications, weekly digests, and product updates through the same infrastructure. With Postmark, the weekly digest is a policy violation.
Ark has no email type restrictions. You can send transactional, marketing, or any other email through the same API. Deliverability is protected through tenant isolation rather than content restrictions. Each tenant's sending reputation is independent, so one tenant's marketing email doesn't affect another tenant's transactional deliverability.
Different philosophy, same goal: protecting deliverability. Postmark restricts content. Ark isolates tenants.
Postmark email policy
Ark email policy
Deliverability protected through tenant isolation, not content restrictions
Who should switch to Ark
Teams hitting stream limits
You've outgrown 10 message streams per server and the workarounds — multiple servers, shared tokens, manual coordination — are slowing you down.
Platforms needing marketing email
Your customers need to send product updates, digests, and marketing email through your platform. Postmark's transactional-only policy means you need a second provider.
Domain onboarding overhead
You're spending support hours helping customers configure DNS records. You need guided, per-provider onboarding that your customers can follow independently.
Per-customer billing needs
You need per-tenant usage data for billing, reporting, and capacity planning. Postmark's server-level metrics don't break down cleanly per customer.
White-label platforms
You need email infrastructure that's invisible to end users. Your customers see their own domains, analytics, and deliverability — not your provider.
Tenant isolation on all plans
You need per-tenant suppression lists, webhooks, and credentials from day one, not just on premium tiers. Ark includes full isolation on every plan.
When Postmark is still the right choice
We have genuine respect for what Postmark has built. They're not a competitor we dismiss lightly. For certain use cases, Postmark is the better choice.
If you're a single company sending transactional email, Postmark excels here. Fifteen years of sender vetting, clean infrastructure, and a transactional-only policy mean your password resets and order confirmations will reach the inbox. This is what they were built for and they do it exceptionally well.
If deliverability is your only priority, Postmark's reputation is earned through discipline. Their strict content policies and careful IP management give them one of the highest inbox placement rates in the industry. If you don't need multi-tenant features, that track record is hard to match.
If you have no multi-tenant needs, Postmark's server-and-streams model is clean and intuitive for a single organization. You don't need tenant isolation, per-customer billing data, or automated domain onboarding. Postmark's simplicity is a feature, not a limitation, in this context.
If you value a large SDK ecosystem, Postmark supports official libraries for Rails, .NET, Java, PHP, Node.js, and Elixir, plus community libraries for many more. If your stack aligns with their ecosystem, integration is smooth.
Note: Postmark was acquired by ActiveCampaign in January 2022. The product continues to operate independently, but it's worth noting as part of your evaluation.
Also compare
What migrating from Postmark looks like
The migration from Postmark to Ark is straightforward. Both use REST APIs with similar patterns, and the concepts map cleanly.
Map Postmark servers to Ark tenants
Each Postmark server that represents a customer becomes an Ark tenant. Create tenants via the API or dashboard. Attach metadata to store your internal customer IDs and any Postmark server references.
Add and verify sending domains
Use the API to add each customer's domain to their tenant. Ark returns exact DNS records needed. If domains were already authenticated on Postmark, much of the DNS work may already be done.
Update your sending code
Replace Postmark API calls with Ark's REST API or SMTP endpoint. Both use similar REST patterns. If you use Postmark's SMTP integration, the switch is a configuration change.
Set up webhooks
Configure platform-level webhooks for all tenants, or per-tenant webhooks for customers that need their own endpoints. Events cover delivery, bounces, opens, clicks, and complaints.
Migrate suppression lists
Export suppression lists from Postmark servers and import them per-tenant in Ark. This preserves bounce and complaint history so you don't accidentally re-send to suppressed addresses.
Most teams complete the migration in a few days for the integration work, plus whatever time their customers need to update DNS records. Since both APIs follow similar REST conventions, the code changes are typically minimal.
FAQ
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