Overview

Postmark is application email infrastructure for sending and tracking messages through an API or SMTP. It suits developers and product teams that need transactional email, with broadcast sending kept separate; its main compromise is a small free allowance and paid charges for volume beyond plan quotas.

Made by a Chicago-based company founded in 2010, Postmark supports inbound processing as well as outbound delivery. Its claim that transactional messages can be sent up to four times faster than other providers is a maker claim, not a guarantee for every application.

Key features

Teams can send through REST API, SMTP, or multi-region SMTP routing. Official libraries cover Node.js, Python, Rails, Ruby, PHP, and .NET; broader integrations include Slack, Zapier, Stripe, WordPress, Supabase, Bubble, Craft CMS, Netlify, and Gravity Forms. SDKs, migration guides, dynamic API documentation, and event webhooks give developers several routes into an existing stack.

Transactional and promotional email run through separate Message Streams and IP infrastructure. That distinction is useful when password resets and receipts should not share a sending path with campaigns. Inbound messages can be converted to JSON and posted to a webhook URL, a practical fit for apps that need to process replies or submitted email programmatically.

Responsive editable templates cover common transactional messages such as welcome emails, password resets, receipts, invoices, and invitations. Tracking includes delivery, bounces, spam, opens, and link activity. Full message content is retained for 45 days by default, with customization available; that default is a meaningful limit for teams that need older message records.

Postmark supports TLS and HTTPS, DKIM, SPF, DMARC, two-factor authentication, API permission controls, penetration testing, and DDoS protection. Its primary data and servers use Deft and AWS, with redundant API, SMTP, inbound, and web servers; the Deft data center is SOC 2 Type 2 accredited. Security is broad, though a dedicated IP is a paid option rather than part of the entry plan.

Message limits also matter for implementation: each email can be no larger than 10 MB including content, headers, and attachments, and can go to at most 50 recipients across To, CC, and BCC. Postmark supports email, live chat, and one-on-one calls, and says customer success support is included without a premium-support fee.

Pricing

The free Developer plan costs 0.00 USD per free and allows 100 emails per month. It never expires and does not permit overages, making it suitable for evaluation or very low-volume use, but not for a growing production service. The free trial also requires no credit card.

Basic costs 15.00 USD per month, billed monthly, and starts at 10,000 emails monthly. It includes five custom sending domains, unlimited emails per day, 45-day retention, and extra emails at $1.80 per 1,000. Up to four users can use Basic. This is the leanest paid fit for a single application that can work within the default history window.

Pro costs 16.50 USD per month, billed monthly, for a starting 10,000 emails monthly. It raises the extra-email rate to $1.30 per 1,000, allows ten custom sending domains and up to six users, extends retention up to 365 days, and adds inbound email processing. For just $1.50 more than Basic at the entry price, those additions make it the more capable choice for teams processing incoming mail or keeping longer message history.

Platform costs 18.00 USD per month, billed monthly, and starts at 10,000 emails monthly. It charges $1.20 per 1,000 extra emails, supports unlimited custom sending domains and users, and includes up to 365 days of retention and inbound processing. It is the natural tier for larger teams or many sending domains; smaller teams may not need its expanded allowances.

Unused emails do not roll over, and paid-plan extra email charges are calculated at the end of the billing cycle. Unlimited emails per day does not remove the monthly quota. Annual plans are not currently offered. Custom activity retention starts at $5 /month and is available only on Pro plans or higher; DMARC monitoring starts at $14 /month per domain. Dedicated IPs start at $50 /month per IP, require at least 300,000 emails per month, and are available on Pro plans or higher. High-volume plans use custom pricing.

Platforms

Postmark is available through API and web. Its iOS app was sunset in June 2025 and is no longer supported, so teams seeking a maintained iOS app should not choose it on that basis.

Who it's for

Postmark is a strong fit for developers building application email flows who value separate transactional and broadcast infrastructure, delivery event visibility, and webhook-based inbound processing. The free tier can support a small evaluation, while Basic through Platform provide a clear path as volume, retention needs, sending domains, or team size increase.

It is less suitable for a project that needs a generous no-cost production quota, annual billing, or an included dedicated IP. The 100-email free cap is restrictive, and paid users must budget for overages rather than relying on unused quota later.

Pros and cons

Separate transactional and promotional infrastructure: Keeps product-critical messages apart from campaign sending.
Useful integration and tracking toolkit: API and SMTP options, SDKs, event webhooks, and delivery, bounce, spam, open, and link tracking support application workflows.
Inbound processing on Pro and above: Converts incoming email to JSON for webhook handling, but is not included in Basic.
Low free ceiling: 100 emails monthly with no overages is enough for evaluation, not meaningful production volume.
Quota charges and no rollover: Extra sending is billed at plan-specific rates, and unused emails expire at the billing boundary.
Retention varies by tier: Basic stops at 45 days by default, while longer retention requires Pro or higher; custom retention also costs extra.

Alternatives

For a wider look at this category, compare Email Deliverability Software and Transactional Email Software.

Choose EasyDMARC instead if a freemium service centered on DMARC monitoring is a better fit; its free plan includes 1,000 emails monthly, one domain, 14 days of data history, and one invited user.

GlockApps is another freemium option, with a free tier combining spam test credits, DMARC message capacity, domain coverage, uptime monitors, and an IP reputation monitor.

Consider TrueSend if a free plan with a 6,000-email monthly allowance, sending domains, a drag-and-drop builder, templates, and basic analytics better matches your needs.

SenderSignal is another freemium alternative with a web platform.

MailMonitor instead is a paid deliverability service with an annual starting price of 1000.00 USD for its Deliverability Foundation.

Pick Warmup Inbox when inbox warmup is the priority: its Basic plan is 15.00 USD per month for one inbox, with 75 warmup messages per day and replies up to 25%.

Mailreach combines email warming and spam testing in its All-In-One plan, priced at 19.50 USD per month with at least 20 spam test credits and up to 100 emails per day.

Mail-Tester is a freemium web alternative.

Verdict

Choose Postmark for application email when dependable separation between transactional and promotional sending, delivery tracking, and developer-facing integration options matter more than a large free allowance. Look elsewhere if your production needs must fit a no-cost plan, if annual billing is essential, or if a dedicated IP must be included without meeting its volume threshold and paying separately.

	Postmark	Sidemail
Free plan	Yes	No
Free trial	Yes	Yes
Paid from	$5/mo	—
Open source	No	No
Platforms	api, Web	Web
Free plan	Yes	No
Paid from	15 /mo	—
Dedicated IP option	Yes	—
Monthly send limit	10,000 emails/mo	2,000 emails/mo
Delivery methods	—	smtp

Postmark vs Sidemail

Postmark

Sidemail