Email Radar
Which email API is best for 10,000 emails?
Amazon SES costs $1.60 for 10,000 emails. Mailgun Basic and Postmark Basic each charge $15, and Resend's first paid tier is $20. Picking the best email API at this volume is a trade: SES wins on price, Postmark on setup.
What matters
- At 10,000 emails a month, Amazon SES Essentials costs roughly $1.60; Mailgun Basic and Postmark Basic each cost $15.00; Resend Pro costs $20.
- Postmark sells three tiers at the same 10,000-email volume: Basic $15.00, Pro $16.50 with inbound processing, Platform $18.00 per month.
- MailRoute reports that since November 5, 2026 Outlook.com has been rejecting part of the mail from domains with no DMARC record, including low-volume senders.
- Resend's first paid tier carries a 50,000-email quota, so a 4,000-email sender pays $20 for capacity it will not use.
What an email API is, and which four I priced
An email API is a service that sends transactional messages for your application, such as password resets, receipts and alerts, over HTTPS or SMTP, then reports delivery, bounces and complaints back by webhook. It is not a newsletter platform: you bring the template and the trigger, the provider owns the sending infrastructure and the reputation work.
I put four providers on the same workload: 10,000 emails a month, sent from a custom domain you authenticate yourself. Every rate below was read on the provider's own pricing page on November 9, 2026. Amazon SES, Mailgun, Postmark and Resend all publish their prices for that volume, so none of this depends on a sales quote.
What 10,000 emails a month costs at each provider
The table below is the whole price surface at that volume, not a headline rate. Included volume, overage rate and free tier all matter, because providers quote different units: Mailgun's "from $1.80 / 1,000" is the price of emails beyond the 10,000 included in Basic, not the price of the plan.
Amazon SES is billed per email with no included allowance. Its Essentials plan lists $0.16 per 1,000 emails for the first 10 million a month, so 10,000 emails comes to about $1.60. Mailgun Basic includes 10,000 for $15 a month and charges from $1.80 per 1,000 after that. Postmark Basic matches it at $15.00, with extra emails at $1.80 per 1,000.
Resend approaches the volume from the other direction. The free plan covers 3,000 emails a month with a 100-per-day cap, and the first paid tier, Pro, is $20 for 50,000 emails. Mailgun's free plan allows 100 emails a day; Postmark's Developer plan allows 100 emails a month and does not expire.
The catch: Outlook now checks DMARC, including on small senders
On November 5, 2026, Outlook.com, Hotmail, Live and MSN started rejecting a share of the mail sent from domains that publish no DMARC record, according to MailRoute's account of its own outbound logs. The bounce reads "550 5.7.1 Message rejected: Message lacks SPF/DKIM/DMARC Auth Records", with a per-message code appended on later rejections.
Microsoft's published policy is narrower than that behaviour. The Outlook.com postmaster page states that since May 5, 2025, domains sending more than 5,000 emails a day must pass SPF, DKIM and DMARC, with non-compliant mail routed to junk and later rejected. MailRoute says the November rejections reach senders well below that threshold, arrive only intermittently, and were not announced.
DMARC is the record that ties your From domain to SPF or DKIM. Amazon's SES documentation describes it as domain alignment with at least one of SPF and DKIM. That detail decides whether your provider choice saves you: a provider can sign mail and still fail DMARC if the signature belongs to the provider's domain. MailRoute notes Microsoft 365 signs with onmicrosoft.com until DKIM is switched on for your own domain.
Who each provider fits
- Amazon SES wins on unit price and loses on hand-holding. Essentials carries no monthly platform fee, so 10,000 emails costs about $1.60. Pro adds a $105 monthly platform fee, $0.22 per 1,000 emails, managed dedicated IPs and deliverability monitoring.
- Mailgun bundles email validation on the same bill: $1.20 per 100 validations on Basic and Foundation, while Scale includes the first 5,000 and charges $0.80 per 100 after that. Extra dedicated IPs cost $59 per IP per month.
- Postmark separates inbound from outbound. At 10,000 emails, Basic is $15.00, Pro is $16.50 and adds inbound email processing, and Platform is $18.00 for more domains and unlimited users. DMARC Digests, its authentication monitoring add-on, starts at $14 per domain per month.
- Resend targets developers who want a small SDK surface: 3,000 emails free, then $20 for 50,000. Add-ons cost $30 a month for a dedicated IP, $20 a month for 100 extra domains and $150 a month for single sign-on.
Where the sticker price misleads
Monthly platform fees dwarf per-email savings at small volumes. SES Essentials at 10,000 emails costs $1.60; moving to Pro for dedicated infrastructure costs $105 a month plus $0.22 per 1,000, or roughly $107 for the same 10,000 emails. That is more than seven months of Mailgun Basic.
Dedicated IPs are the other cliff. Postmark's start at $50 per month per IP with a 300,000-emails-a-month minimum. Mailgun charges $59 per IP per month. Resend sells one as a $30 monthly add-on, limited to customers sending more than 3,000 emails a day on Scale.
Then there is quota granularity. Resend jumps from 3,000 free emails to a 50,000-email tier, so a sender at 4,000 emails pays $20 for capacity it never uses. Mailgun's ladder is smoother at this end: $15 for 10,000, $35 for 50,000, $90 for 100,000, with overage rates falling from $1.80 to $1.10 per 1,000 as the tier rises.
What to do before you choose a provider
Fix authentication first, because it is the one thing no provider can do for you without your DNS. Publish a DMARC record at p=none, which declares the policy without asking receivers to act on failures, and confirm that either SPF or DKIM passes for the exact domain in your From address. Then pick on price and control.
- Check whether your domain publishes DMARC at all: a TXT lookup that returns nothing starting with v=DMARC1 means it does not.
- Turn on DKIM signing for your own domain inside the provider, not the provider's shared domain.
- Compare the providers at your real monthly volume, not at the tier you hope to grow into.
Among the four, SES is the cheapest way to send 10,000 authenticated emails and the least forgiving if your DNS is wrong. Postmark and Mailgun cost about ten times more at that volume and give you a support queue, templates and diagnostics in return.
At a glance
| Provider | Cheapest paid tier at 10,000 emails | Included volume | Extra emails | Free tier |
|---|---|---|---|---|
| Amazon SES (Essentials) | About $1.60/mo, billed per email | None | $0.16 per 1,000 | Not listed in the plan table |
| Mailgun (Basic) | $15/mo | 10,000 | From $1.80 per 1,000 | 100 emails/day |
| Postmark (Basic) | $15.00/mo | 10,000 | $1.80 per 1,000 | 100 emails/month |
| Resend (Pro) | $20/mo | 50,000 | $0.90 per 1,000 | 3,000/month, 100/day |
FAQ
Is Amazon SES cheaper than Mailgun and Postmark?
Yes, by roughly ten times at 10,000 emails a month. SES Essentials lists $0.16 per 1,000 emails, or about $1.60, while Mailgun Basic and Postmark Basic each include 10,000 emails for $15. SES charges for infrastructure only, and its Pro plan adds a $105 monthly platform fee.
Which email API has the best free tier?
Resend gives the most volume: 3,000 emails a month with a 100-per-day cap. Mailgun's free plan allows 100 emails a day, and Postmark's Developer plan allows 100 emails a month with no expiry.
Does Outlook reject email from domains without DMARC?
MailRoute reports partial rejections since November 5, 2026, with the 550 5.7.1 error citing missing SPF, DKIM or DMARC records. Microsoft's published rule still names domains sending more than 5,000 emails a day, so the safe move for any sender is to publish a DMARC record at p=none and make sure SPF or DKIM aligns with the From domain.
Related reading
SendGrid alternatives, Resend pricing, What does SendGrid pricing actually cost in 2026?