InboxGreen vs Mailgun

Email sending API vs email authentication diagnostics - what each one actually does for your deliverability.

Short answer: Mailgun is a developer-focused email sending API - you integrate it to send transactional and marketing emails from your application. InboxGreen is an email authentication tool - you use it to check and fix the DNS records (SPF, DKIM, DMARC) that determine whether those emails reach the inbox. Mailgun sends your email. InboxGreen makes sure the DNS is configured so it gets delivered.

Mailgun

Email sending API

Send transactional and marketing emails via REST API or SMTP relay. Built for developers. Includes email validation API, webhooks, inbound routing, and detailed delivery logs.

Free: 100 emails/day (trial period)

Paid from $15/month (50,000 emails)

InboxGreen

Email authentication diagnostics

Check SPF, DKIM, and DMARC for your sending domain. Get copy-paste DNS fix records. Works alongside Mailgun and any other sending platform.

Free check - no account needed

FixKit $29 one-time - Monitor from $19/mo

Feature comparison

FeatureInboxGreenMailgun
Send transactional and marketing email via API No Yes - REST API and SMTP relay
Check SPF / DKIM / DMARC in DNS Yes - free, instant, no account No standalone DNS authentication check
Generate copy-paste DNS fix records Yes - formatted per DNS provider No
DKIM setup for your sending domain Check + generate DKIM records free Sets up DKIM via CNAME for custom sending domains
SPF record generator Free - try it No
DMARC record generator Free - try it No
Email validation API No Yes - real-time email validation endpoint
Delivery events and webhooks No Yes - opens, clicks, bounces, complaints via webhooks
Inbound email routing No Yes - route inbound emails to URLs or forward
Ongoing DNS monitoring + alerts Yes - from $19/mo No
Blacklist check Free - try it No
No account required Yes - free tools work without signup Account required for all use

Why Mailgun emails go to spam - and what actually fixes it

Mailgun handles sending, but the DNS authentication records that determine deliverability live on your domain - not inside Mailgun. The most common reasons Mailgun emails land in spam are DNS problems, not Mailgun problems:

  • SPF not updated - Your SPF record must include include:mailgun.org. Many developers never add this when first integrating Mailgun.
  • DKIM not verified in Mailgun - Mailgun provides CNAME or TXT records for DKIM, but they only activate once published in your DNS. Many domains have Mailgun configured but DKIM not actually published.
  • No DMARC record - Without DMARC, mail servers receiving your email have no enforcement policy. Gmail requires DMARC for bulk senders.
  • Sending from a subdomain without separate authentication - Using a subdomain like mg.yourdomain.com for Mailgun is common, but that subdomain needs its own SPF, DKIM, and DMARC configuration.

A free InboxGreen check identifies all of these in seconds and tells you exactly what to fix.

search Check My Domain Free

When you only need Mailgun

  • You are a developer building email sending into an application and need a reliable API.
  • Your domain authentication (SPF, DKIM, DMARC) is already set up and emails are reaching the inbox.
  • You need delivery logs, webhooks, inbound routing, or email validation API features.

When to use InboxGreen alongside Mailgun

  • Your Mailgun emails are landing in spam or being deferred by receiving servers.
  • You need to verify that SPF includes mailgun.org and Mailgun's DKIM records are live in DNS.
  • You want to set up DMARC so Gmail and Yahoo accept your mail and your domain is protected.
  • You want ongoing monitoring that alerts you if DNS records break after a deployment or DNS migration.
Mailgun emails going to spam? Check your domain authentication first.
A free InboxGreen check will show whether SPF, DKIM, and DMARC are correctly configured for your sending domain.
search Run Free Domain Check tune SPF Generator

Frequently asked questions

Why are my Mailgun emails going to spam?

The most common causes are SPF not including include:mailgun.org, DKIM records not published in DNS (Mailgun requires you to add CNAME or TXT records yourself), no DMARC policy, or Mailgun configured on your root domain when it should be on a dedicated sending subdomain. Run a free InboxGreen check on your sending domain to identify exactly what is misconfigured.

What SPF record do I need for Mailgun?

Add include:mailgun.org to your SPF record. A basic record looks like:
v=spf1 include:mailgun.org ~all
If you send from other services too (Google Workspace, etc.), include them as well. Use the SPF Generator to build it correctly. If you use a Mailgun sending subdomain (e.g. mg.yourdomain.com), the SPF record goes on that subdomain, not your root domain.

Does Mailgun set up SPF and DKIM automatically?

Mailgun provides the DKIM records (CNAME or TXT) that you must publish in your own DNS. It does not manage SPF for you. Mailgun's domain verification panel will show whether DKIM and SPF are detected, but it does not check your overall DMARC configuration. Use InboxGreen for a complete picture of all three.

Should I send Mailgun emails from a subdomain?

Using a dedicated sending subdomain like mg.yourdomain.com or mail.yourdomain.com is a common Mailgun setup. It isolates your transactional email reputation from your root domain. When using a subdomain, the SPF, DKIM, and DMARC records must be set up on that subdomain, not just the root domain. Run an InboxGreen check on the subdomain to confirm everything is correctly configured.