Mailgun and Warmup Inbox are deliverability services for developers and outbound senders. Mailgun is built to send the email an application fires on its own, with address validation and rendering previews sold in the same account. Warmup Inbox exists to warm up mailboxes before cold outreach. Developers and teams wanting one account suit Mailgun, while agencies and sales teams suit Warmup Inbox.
Pricing: Free for 100 emails/day; Send from $15/mo for 10,000 emails; Optimize add-on from $49/mo; Inspect add-on from $99/mo. Billed monthly only.
Mailgun is a transactional email API and SMTP relay for developers, with paid add-ons for deliverability monitoring, pre-send QA and email validation.
Pricing: Per inbox, per month: Basic $15 (75 warm-ups/day), Pro $49 (250/day), Max $79 (1,000/day). 15+ inboxes need a Custom quote. 7-day trial, no card.
Warmup Inbox builds a mailbox's sender reputation with real traffic across a 30,000+ inbox network, then reports placement and reputation, priced per inbox.
Email Deliverability Tools features side-by-side
Free for 100 emails/day; Send from $15/mo for 10,000 emails; Optimize add-on from $49/mo; Inspect add-on from $99/mo. Billed monthly only.
Per inbox, per month: Basic $15 (75 warm-ups/day), Pro $49 (250/day), Max $79 (1,000/day). 15+ inboxes need a Custom quote. 7-day trial, no card.
Choose Mailgun if you are coding an app that has to deliver its own receipts and alerts. Choose Warmup Inbox if you run cold outreach and need new mailboxes warmed first. Mailgun offers a free plan before its monthly paid plans. Warmup Inbox bills monthly too, and its higher plans come by quote.
A developer wiring email into software gets a sending API and an SMTP relay from Mailgun. The product also turns DMARC aggregate reports into a dashboard of sending sources and pass rates. Bounce and complaint rates are tracked per stream, with alerts past a threshold. One limit is that the calling software decides what goes out, and drag-and-drop newsletters are left to Mailjet, a sister product.
Cold outreach teams and agencies start from a different problem, a new mailbox nobody trusts yet. Warmup Inbox exchanges real traffic across a network of inboxes to build that reputation automatically. Tests can run on real campaigns because the service connects to sending platforms such as HubSpot or Klaviyo. Warmup Inbox works next to your mailbox provider and sending platform, and replaces neither.
Mailgun's users praise quick support, even on the free plan, and mail that arrives well once integrated. They complain that accounts or domains get disabled or locked with slow resolution, and that support is slow or unhelpful on setup problems. Reviewers of Warmup Inbox like personal support and simple setup, and some see better inbox placement after warming. Other reviewers of Warmup Inbox describe mailboxes suspended by Google or Microsoft soon after connecting, little visible improvement with slow support, and confusing billing.
Mailgun describes an ecommerce marketing platform that needed email delivery and domain verification at scale, and the platform dropped a verification email step it no longer needed. Warmup Inbox describes a B2B ecommerce company that connected Outlook and Zoho mailboxes and paired warm-up with the spam word checker and placement tests. Afterward the company saw deliverability rise and open rates improve.
Looking for more options?
Browse all Email Deliverability Tools
