The honest Inbox OSS vs Mailgun comparison

Pricing: Inbox OSS vs Mailgun

Mailgun uses per-tier feature gating. The Foundation plan is $35 per month for 50,000 messages and excludes most deliverability tooling. Growth is $80 per month for 100,000 messages. Scale is $90 per month for 100,000 messages plus HIPAA compliance. Marketing automation is restricted to higher tiers and requires the separate Mailgun Optimize add-on. Validation runs through Mailgun Validations, a separate product billed per check.

Inbox OSS uses transparent volume-based pricing with every feature in every tier. Essentials is $19 per month for 50,000 messages and includes marketing campaigns, automations, validation credits, and webhooks. Pro is $89 per month for 500,000 messages and includes one fully warmed dedicated IP. For a 50,000 message workload, Inbox OSS Essentials at $19 is approximately 45 percent cheaper than Mailgun Foundation at $35 — and the Inbox OSS plan includes marketing automation that Mailgun does not include at any tier below Scale.

For HIPAA-regulated workloads, Mailgun Scale ($90/mo) provides the BAA at the higher tier. Inbox OSS reserves HIPAA BAA for Enterprise (custom pricing), which typically lands at similar cost for true high-volume HIPAA senders but provides better unit economics for organizations sending under 500k messages per month with HIPAA requirements.

Deliverability: Inbox OSS vs Mailgun

Mailgun's deliverability is strong on higher tiers — Foundation customers receive the baseline shared-pool experience, while Growth and Scale customers get dedicated reputation monitoring, deeper SMTP error reporting, and access to the Mailgun deliverability consulting team. Mailgun Optimize provides inbox-placement testing as an add-on product.

Inbox OSS includes inbox-placement testing as a standard feature on every paid plan, ships adaptive per-IP warmup automation (Mailgun's warmup is manual schedule-based), and runs Spamhaus Zen + Barracuda real-time blocklist monitoring included in every tier. The 7-check email validation engine is included with monthly validation credits at every tier; Mailgun Validations bills separately.

For high-volume senders, the most meaningful deliverability difference is bounce-rate prevention. Inbox OSS customers using pre-send validation report average bounce rates under 0.5 percent on cold acquisition lists. Mailgun customers using Mailgun Validations as a separate product see similar bounce rates but pay separately for the validation calls.

Migrating from Mailgun to Inbox OSS

Inbox OSS provides a Mailgun-compatible v3/messages endpoint that accepts the Mailgun form-encoded request body verbatim. The migration path:

1. Change the base URL from api.mailgun.net/v3 to api.inbox.onesourcesoft.com/api/v1 in your Mailgun SDK or HTTP client configuration.
2. Replace your Mailgun API key with your Inbox OSS API key (still passed via the same Basic auth or Bearer header).
3. Update your sending domain CNAMEs to point at Inbox OSS authoritative DNS (we generate the DKIM keys and provide the records).

Mailgun routes, suppression lists, webhooks, and templates can all be exported from Mailgun and imported into Inbox OSS. We accept the Mailgun suppression CSV format verbatim, the Mailgun HMAC-SHA256 webhook signature scheme (in addition to our recommended Ed25519), and Mailgun's Handlebars template dialect.

For Enterprise migrations we provide a dedicated migration architect who runs the parallel-traffic playbook and stays on Slack with your team through cutover week. Free migration support is included on all Inbox OSS paid plans.

When Mailgun might be the better choice

Mailgun is a good fit if you are deeply integrated with the broader Sinch communications platform (SMS, voice, conversational AI) and want consolidated billing. Mailgun's API surface for inbound routing and the Mailgun Routes product has some unique features around mailing-list operations that we are still building toward.