Troubleshoot Mailgun in EonMailer

401 Forbidden

• Invalid API key or using public key instead of private.
• Wrong API base for region — EU domain requires EU endpoint.

404 Domain not found

• Typo in domain string vs Mailgun dashboard.
• Domain created in different Mailgun account.

DNS verification stuck

• Run dig on TXT/CNAME hosts Mailgun lists.
• Remove duplicate SPF records.
• Cloudflare proxy on CNAME — set DNS only.

402 Payment required

• Billing card expired — Mailgun stops sending until updated.

Events not syncing

• Webhook URL HTTP not HTTPS.
• Firewall blocking Mailgun IP ranges (rare) — allow documented IPs.

550 relay denied

• From domain not on verified Mailgun domain.
• Sandbox domain (sandboxXXX.mailgun.org) used in production — add custom domain.