Why is Mailgun giving me so many bounce issues?

Mailgun usually isn’t the root cause of bounces — it’s the sender setup, list quality, or recipient-side filtering. The most common reasons are:

1) Bad or stale email list

• Old addresses
• Typos (gmial.com, hotmial.com)
• Role accounts or disposable addresses
• People who never opted in

2) Low sender reputation

If Mailgun is sending from a domain or IP with poor reputation, providers like Gmail, Outlook, Yahoo, etc. may reject or spam your mail.

Common causes:

• Sudden volume spikes
• High complaint rates
• Too many previous bounces
• New domain/IP with no warmup

3) DNS/authentication problems

If your domain isn’t properly authenticated, delivery rates drop and bounces increase.

Check:

• SPF
• DKIM
• DMARC
• Valid Mailgun sending domain setup

4) Content triggers

Some messages get rejected because of:

• Spammy subject lines
• URL shorteners
• Too many links
• Suspicious attachments
• HTML that looks malformed or phishy

5) Recipient server issues

Sometimes the destination mail server is rejecting mail due to:

• Full mailbox
• Greylisting
• Temporary outages
• Strict anti-spam policies

6) You may be confusing bounces with other failures

Mailgun often reports:

• Bounce = permanent failure
• Temporary failure / deferred = retryable issue
• Spam complaint / unsubscribe = different problem, but related to deliverability

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What to check first

1. Look at the bounce reason in Mailgun logs
   • The SMTP error text usually tells you why.
2. Check your domain authentication
3. Inspect your recipient list quality
4. Look for patterns:
   • Specific provider? (Gmail, Microsoft, Yahoo)
   • Specific domain?
   • Only certain campaigns?
5. Check whether your sending volume recently changed

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If you want, I can help you diagnose it quickly

Paste one or two example bounce messages from Mailgun, and I can tell you what they mean and what to fix.