Mailgun vs Postmark: what 20,000 emails a month actually costs

Both vendors quote $15 for 10,000 emails, which makes them look interchangeable at the entry point. The difference appears at the overage line, where one vendor sells a second tier at a lower marginal rate and the other sells a bigger bucket.

At 20,000 emails a month the totals are $33.00 on Mailgun Basic, $33.00 on Postmark Basic, $29.50 on Postmark Pro and $30.00 on Postmark Platform. Mailgun's $35 Foundation tier includes 50,000 emails and only wins above roughly 21,100.

Entry tiers and what 20,000 emails costs

Mailgun also sells Scale at $90 for 100,000 emails with a sliding overage rate that falls to $0.50 per 1,000 at a million. Postmark has no equivalent volume tier, which is why its three plans all sit between $15 and $18.

What the numbers actually mean

The two vendors price the same way at the bottom and diverge immediately above it. Mailgun's answer to needing more than 10,000 emails is a larger included bucket: Foundation at $35 for 50,000. Postmark's answer is a better marginal rate on the same bucket: Pro at $16.50 with $1.30 per 1,000 extra.

That makes Postmark cheaper for the band between 10,000 and 50,000 emails a month, and Mailgun cheaper from the point where Foundation's flat $35 undercuts a metered bill. At 40,000 emails, Postmark Pro is $16.50 + 30 x $1.30 = $55.50 while Mailgun Foundation is $35.00. At 20,000 the ordering reverses: $29.50 against $35.00.

The per-1,000 view shows how each vendor moves. Mailgun Basic and Postmark Basic both charge $1.50 per 1,000 at their 10,000-email allowance and $1.80 beyond it. Postmark then cuts the marginal rate instead of the base — $1.30 on Pro, $1.20 on Platform — which is why Mailgun's Foundation tier wins at 50,000 emails with a flat $35.00 while Postmark pays $66.00, and why Postmark reaches $126.00 at 100,000 emails where Mailgun's Scale tier is $90.00.

The free tiers are not comparable products. Mailgun gives 100 emails a day, which is a development allowance that can carry a small production site. Postmark gives 100 emails a month and states plainly that no overages are allowed and that it sells nothing between that and 10,000 — so the real entry price at Postmark is $15, not $0.

How we measured it

Every price, allowance and overage rate is quoted from the Mailgun and Postmark pricing pages, both opened on 2026-10-25. Postmark's page prices plans against a volume selector that defaults to 10,000 emails, so the 20,000-email column was computed from the published per-1,000 rate rather than read off the page; those figures are marked calculated. Nothing was sent and no deliverability test was run.

What changes in practice

Per-1,000 pricing hides how billing actually behaves. Postmark charges overage per 1,000 emails and does not roll unused emails over between months, so a seasonal sender pays for the peak month and starts the quiet month from zero.

Mailgun's tier structure is worth checking before a launch, because the next bucket up can be cheaper than the overage on the current one. Basic at 25,000 emails is $15 + 15 x $1.80 = $42.00, while Foundation is $35.00 for 50,000 — the upgrade pays for itself and adds headroom.

Both vendors gate the features that matter at volume. Postmark offers dedicated IPs only from 300,000 emails a month, and Mailgun's dedicated IP pools sit on the Scale tier at $90 a month, so the headline per-1,000 rates do not describe what a serious sender ends up paying.

Retention separates them as capability rather than money. Postmark keeps 45 days of message data on Basic and lets Pro extend it to a customizable 365 days, while Mailgun keeps one day on Free and Basic, five days on Foundation and thirty on Scale. That choice decides whether last month's delivery problem can still be investigated at all.

Bottom line

At 20,000 emails a month, Postmark Pro is the cheapest published option at $29.50, and Mailgun's best value is Foundation at $35.00 once volume passes about 21,100 emails. Below 10,000 emails a month the decision is about the free tier, and Mailgun's 100-a-day allowance is the only one of the two that can carry live traffic.