Overview

Postmark is application email infrastructure for software teams sending transactional and broadcast messages. It suits developers who want API or SMTP delivery, delivery-event tracking, and a way to process incoming mail. Its strongest distinction is the separation of transactional and promotional traffic; its small free allowance and metered paid volume make it less compelling for high-volume sending on a fixed budget.

Key features

Messages can be sent through a REST API, SMTP, or multi-region SMTP routing. Official libraries cover Node.js, Python, Rails, Ruby, PHP, and .NET, while integrations include Slack, Zapier, Stripe, WordPress, Supabase, Bubble, Craft CMS, Netlify, and Gravity Forms. Migration guides, dynamic API documentation, and event webhooks give development teams practical paths for connecting delivery to an existing application.

Transactional and broadcast mail run through separate Message Streams and IP infrastructure. That separation is useful when password resets and receipts should not share a sending path with promotional campaigns. Postmark also converts inbound messages into JSON and posts them to a webhook URL, a meaningful advantage for applications that need to act on replies or other incoming mail.

Responsive, editable templates cover common transactional messages such as welcome emails, password resets, receipts, invoices, and invitations. Tracking covers delivery, bounces, spam, opens, and links. The message-content history is retained for 45 days by default, with customization available; the Pro and Platform plans extend retention up to 365 days. Each email can be no larger than 10 MB including headers, content, and attachments, and a message can go to at most 50 recipients across To, CC, and BCC.

Security controls include TLS and HTTPS, DKIM, SPF, DMARC, two-factor authentication, API permissions, penetration testing, and DDoS protection. Postmark says its infrastructure has redundant API, SMTP, inbound, and web servers, and that its Deft data center is SOC 2 Type 2 accredited. Customer support includes email, live chat, and one-on-one calls, without an extra premium-support fee. Postmark's claim that it sends transactional email up to four times faster than other providers should be treated as its own performance claim, not a guarantee for every application.

Pricing

The free Developer plan costs 0.00 USD per free and provides 100 emails per month. It never expires and does not permit overages, so it works for a small prototype or low-volume trial but not for a product that may exceed the cap. The free trial requires no credit card.

Paid plans are billed monthly, with no annual plans currently offered. Basic starts at 15.00 USD per month for 10,000 emails per month, with extra emails at $1.80 per 1,000. It includes five custom sending domains, unlimited emails per day, 45-day retention, and up to four users. For a small team that needs straightforward delivery and tracking, Basic is the lowest-cost paid entry, but its overage rate is the highest of the paid tiers.

Pro starts at 16.50 USD per month for 10,000 emails per month; additional volume is $1.30 per 1,000. It raises the domain allowance to ten, the user limit to six, extends retention up to 365 days, and adds inbound email processing. The small step up from Basic makes Pro the more rounded choice for teams that need inbound handling or longer history.

Platform starts at 18.00 USD per month for 10,000 emails per month, with extra emails at $1.20 per 1,000. It adds unlimited custom sending domains and unlimited users while retaining the extended history and inbound processing. It is the clearest fit for larger teams or multiple applications; smaller teams pay for capacity they may not need. All paid tiers allow unlimited emails per day, but monthly quotas still apply: extra emails are calculated at billing-cycle end, and unused volume does not roll over.

Optional charges include custom activity retention, starting at $5 /month on Pro or higher; DMARC monitoring, starting at $14 /month per domain; and a dedicated IP, starting at $50 /month per IP for customers sending at least 300,000 emails per month on Pro or higher. High-volume plans use custom pricing.

Platforms

Postmark runs on the web and through an API, with SMTP also supported as a delivery method. Its iOS app was discontinued in June 2025 and is no longer supported, so it is not a choice for teams that need an iOS app.

Who it's for

Postmark is a strong fit for developers building application email into a product, especially where transactional messages need separate handling from promotional mail, or where inbound email should trigger application workflows. The API, SMTP options, libraries, templates, and event hooks cover common integration needs. It is less suited to senders needing a generous free volume, predictable all-in pricing above quota, or a supported iOS app.

Pros and cons

Separate transactional and promotional infrastructure: Helps keep product-critical messages distinct from campaigns.
Inbound processing and useful event tracking: Incoming mail becomes webhook-ready JSON, while delivery, bounce, spam, open, and link events are tracked.
Low entry price for paid use: Basic starts at 15.00 USD per month, with Pro only slightly higher for inbound processing and longer retention.
Free use is tightly capped: 100 emails per month and no overages makes the free plan unsuitable for growing traffic.
Volume costs can vary: Extra emails are billed after the cycle, and unused quota does not carry forward.
Plan boundaries matter: More domains, users, inbound processing, and long retention require higher tiers or add-ons.

Alternatives

For focused deliverability monitoring rather than application email delivery, EasyDMARC has a free plan with 1,000 emails per month, one domain, 14 days of history, and one invited user; its DMARC Plus plan is 35.99 USD per month, billed annually. GlockApps is another monitoring-oriented alternative: its free plan includes two spam-test credits, 10,000 DMARC messages, unlimited DMARC domains, five uptime monitors, one IP reputation monitor, and one user.

TrueSend offers a free plan with 6,000 emails per month, two sending domains, a drag-and-drop builder, templates, and basic analytics, making it an option to compare for campaign-oriented sending. SenderSignal, MailMonitor, Warmup Inbox, Mailreach, and Mail-Tester are alternatives to consider when evaluating other email-related tools.

Browse the Transactional Email Software list for more delivery services, or the Email Deliverability Software list for monitoring-focused options.

Verdict

Choose Postmark for application email when clean separation between transactional and promotional traffic, inbound webhook processing, and delivery visibility matter more than a large free quota. Pro is the strongest balance for teams needing inbound mail or extended history; look elsewhere if you need generous free sending or firm costs that do not rise with overages.

	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