Transactional email: cost per 1,000 emails at 1,000, 10,000 and 50,000 a month

Transactional email is priced in tiers, and the tier boundaries matter more than the headline rate: the cheapest provider at 10,000 emails is not the cheapest at 50,000, because one of them stops charging at 50,000 and the others keep metering.

At 10,000 emails a month Postmark and Mailgun both cost $15.00 — $1.50 per 1,000 — and Resend costs $20.00. At 50,000 the order flips: Resend's $20 covers the whole volume at $0.40 per 1,000, against Mailgun's $35.00 and Postmark's $66.00.

What each volume costs

Postmark's figures use its cheapest plan at each volume: Basic at 10,000 and Platform at 50,000, since Platform's $1.20 per-1,000 overage beats Basic's $1.80. Mailgun's use Basic then Foundation, whose 50,000 included emails cover the volume exactly.

What the numbers actually mean

Resend has the strangest curve of the three. Free carries 3,000 emails a month with a 100-a-day cap, and the next step is $20 for 50,000. That means a sender at 5,000 emails a month pays $20 and a sender at 45,000 pays the same $20, so the effective rate falls from $4.00 per 1,000 to $0.44 as volume grows. Past 50,000 the curve flattens back into a metered line: another 50,000 emails cost $45.00 in overage at $0.90 per 1,000.

Postmark's curve is inverted: cheap at the bottom, expensive at the top. Basic is $15 for 10,000 and $1.80 per 1,000 beyond, which is $87.00 at 50,000 before you switch to Platform at $66.00. Both are the same allowance at different marginal rates, so the choice between them is purely a question of how much overage you expect.

Mailgun sits between the two. Basic matches Postmark at $15 and $1.80, but the next tier is a bigger bucket rather than a cheaper marginal rate: Foundation at $35 for 50,000. At exactly 50,000 emails that is $0.70 per 1,000, cheaper than either Postmark tier.

The free tiers are where the per-1,000 number collapses to zero, and they are not equivalent. Resend and Mailgun both meter 100 emails a day, which allows about 3,000 a month. Postmark's free plan is 100 emails a month and forbids overages, so 1,000 emails a month is a $15 bill there and $0 on the other two.

How we measured it

Prices, allowances and overage rates are quoted from the Resend, Postmark and Mailgun pricing pages, all opened on 2026-10-25. Nothing was sent and no deliverability test was run. Each total is the cheapest published plan that covers the volume, plus overage at that plan's published per-1,000 rate where the volume exceeds the allowance; those calculations are marked as such, and the effective per-1,000 figures divide the total by the volume.

What changes in practice

The plan boundary is the risk, not the rate. Resend bills overage only when pay-as-you-go is enabled under Transactional Overages, so a product that crosses 50,000 emails in a launch week stops sending rather than paying $0.90 per 1,000. Postmark charges overage automatically and does not roll unused emails over, so a quiet month does not buy credit for a loud one.

Minimum monthly spend is the second consideration. Postmark's floor is $15 whatever you send, and Resend's is $20 once you exceed 3,000 emails. For a product doing 2,000 transactional emails a month, that is a $180 to $240 annual commitment to a service whose marginal cost is close to nothing.

The third is what the per-1,000 rate excludes. Dedicated IPs, inbound processing, longer retention and higher sending limits all sit on higher tiers, and Postmark gates dedicated IPs at 300,000 emails a month while Resend gates them behind its $90 Scale plan plus a $30 add-on.

Bottom line

Under 10,000 emails a month, Postmark or Mailgun at $15.00 beats Resend's $20.00, and the free daily caps at Resend and Mailgun mean small senders can start at $0. From 20,000 emails upward, Resend Pro's flat $20 is the cheapest published option until 50,000, after which its $0.90 per 1,000 keeps it competitive against Mailgun's $1.30 and Postmark's $1.20.