Resend vs Postmark vs Mailgun vs Postscale — a 2026 comparison
Side-by-side look at four transactional email APIs — pricing, features, EU-compliance posture, and when to pick each.
Every few weeks someone on Hacker News asks "which transactional email API should we use?" and the thread turns into 200 comments of brand loyalty. Here's an opinionated but factual comparison of the four vendors worth naming in 2026, written by someone who builds one of them.
Yes, this is a Postscale blog. I've tried to keep the facts on competitors honest — dates and prices are from public pricing pages as of April 2026. Where Postscale is the right answer I'll say so; where we're not, I'll tell you too.
The four at a glance
| Resend | Postmark | Mailgun | Postscale | |
|---|---|---|---|---|
| HQ | US (Delaware) | US (ActiveCampaign) | US (Sinch) | EU (Estonia, DNScale OÜ) |
| EU-only processing | Replication only | EU Servers add-on | EU region opt-in | Default |
| Starting paid tier | ~$20 / 5k sends | ~$15 / 10k sends | ~$35 / 5k sends | €9 / 10k sends |
| Price at 100k sends | ~$90 | ~$134 | ~$85 | €79 |
| Inbound email API | No | Yes (separate inbox) | Yes (add-on) | Yes (included) |
| Masked addresses | No | No | No | Yes (Shield) |
| DMARC reports API | No | No | Partial | Yes |
| XRechnung / e-invoicing | No | No | No | Yes |
| React Email friendly | Yes (native) | Yes | Works | Works |
| SMTP relay | Yes | Yes | Yes | Yes |
Prices and feature sets will drift; check the relevant pricing page before making a final call.
Where each one shines
Resend
Pick when: you're a small team, Postmark feels like a big old product, and you want something that feels like 2024 software. React Email is a native integration and the DX is the cleanest of the four.
Don't pick when: you need EU-only processing (Schrems II applies), inbound parsing, masked addresses, or XRechnung support. Also: Resend was founded in 2023 — it's the youngest of the four, and some enterprise procurement processes will notice.
Postmark
Pick when: you care about inbox placement above all else, and your team has a multi-year history with Postmark's culture (they're famous for uptime and responsiveness). Their inbound parsing is mature and documented.
Don't pick when: you're cost-sensitive at scale. At 500k sends/month Postmark is ~$654; Mailgun is ~$405; Postscale is €329. If deliverability is great across the board (it usually is), you're paying a big premium for a brand.
Mailgun
Pick when: you need the kitchen sink. Validations API, EU region, dedicated IPs, event store — Mailgun has almost every feature an ESP can sell, though often as paid add-ons. They're also the most forgiving on sending reputation recovery.
Don't pick when: you want simple pricing. Mailgun's add-ons compound, and account-level features (like validations volume) don't carry across environments. Also, acquisition by Sinch has slowed product velocity.
Postscale
Pick when:
- You're EU-based and don't want to do the Schrems II/TIA dance for every new vendor.
- You need more than transactional — if you also want inbound webhooks, masked addresses, DMARC reports, or XRechnung under one key.
- Billing and total cost matter. Flat EUR pricing, no per-feature add-ons.
Don't pick when: you want marketing broadcasts/audiences/campaigns. We don't ship those. Run them on a dedicated tool (Customer.io, Loops, Resend Audiences) and integrate at the unsubscribe level.
Deliverability — the honest take
All four are in the same general tier for inbox placement to major consumer mailboxes. Dedicated IPs help; shared pools are adequate; authentication (SPF + DKIM + DMARC) matters more than the vendor choice. The differences people report are usually (a) sender-reputation issues they'd have with any vendor, (b) IP pool assignments that change over time, or (c) a single bad week that doesn't reflect the steady state.
If you're sending to a niche audience (transactional-only, B2B only, small-business DE/FR), regional IP provenance starts mattering. EU IPs generally see better deliverability into Central European inboxes; US IPs see fractionally better deliverability into US inboxes. Not enough to overturn a vendor pick, but enough to dismiss "EU provider = worse deliverability" as the myth it is.
Pricing — the direct number
Rounded, for one typical production profile:
| Monthly sends | Resend | Postmark | Mailgun | Postscale |
|---|---|---|---|---|
| 10,000 | ~$20 | ~$15 | ~$35 | €9 |
| 100,000 | ~$90 | ~$134 | ~$85 | €79 |
| 500,000 | ~$240 | ~$654 | ~$405 | €329 |
At all three volumes, Postscale is the cheapest of the four, and at volume the delta widens. Taking the cheapest doesn't mean it's the right answer — but if everything else is equal, 40–60% margin on a fixed-cost line matters.
Compliance — the direct answer
If you are an EU-based company selling to EU customers, and your legal team has ever made you sign a TIA (Transfer Impact Assessment), the calculus changes. Resend, Postmark, and Mailgun are US processors. Postscale is an EU processor.
The paperwork difference isn't hypothetical — it's hours per vendor per year. At some point that cost eats into any deliverability or feature advantage.
Bottom line
Three honest answers:
- "We're a US startup, sending transactional, simple stack." → Resend. It's the friendliest modern option for your size.
- "We're mid-market, deliverability is the bottleneck, we've been on Postmark." → Stay on Postmark unless cost or EU-compliance drags you off.
- "We're EU, we want one vendor for sending + inbound + privacy + e-invoicing, and we'd rather pay in EUR." → Postscale. Honestly this is what we built for.
If you want a vendor-specific comparison, we maintain Postscale vs SendGrid, Postscale vs Mailgun, Postscale vs Postmark, and Postscale vs Resend with migration notes.