mailgun '5.7.1 message rejected due to user rules' on agent bulk send

TL;DR

'Rejected due to user rules' means the receiving side's filters bounced the message, not that Mailgun failed to send it. Confirm your domain authentication is intact, check your dedicated IP reputation and complaint rates for the real cause, clean up content patterns that trip recipient filters, and escalate to Mailgun support with message IDs if the rejections persist after the fix.

The query

mailgun '5.7.1 message rejected due to user rules' on agent bulk send

Steps

1. Confirm authentication is intact for the sending domain

Check that SPF, DKIM, and the Mailgun tracking-domain records still resolve. Authentication that silently broke (DNS change, expired DKIM selector) makes recipient filters far more aggressive.

Expected: all Mailgun DNS records resolve correctly.

2. Check IP reputation and complaint rates

In Mailgun analytics, look at the dedicated IP's complaint rate and bounce rate around the time rejections started. A complaint spike or a fresh blocklist listing is the usual underlying cause; the 'user rules' message is just how the receiving provider phrases it.

Expected: you know whether reputation, complaints, or neither drove the rejections.

3. Simplify content that trips recipient-side filters

Test with a plain-text, link-light version of the message. Heavy link tracking, URL shorteners, image-only bodies, and spammy phrasing all feed recipient-side rule engines. Reintroduce elements one at a time to find the trigger.

Expected: the simplified test message delivers; the trigger element is identified.

4. Open a Mailgun support case with message IDs if it persists

If authentication, reputation, and content all check out, collect several rejected message IDs from the logs and open a support case. Mailgun can see the receiving provider's full response, which the bounce summary often truncates.

Expected: support identifies the provider-side rule or confirms delivery is restored.

Use this when

• Mailgun bulk sends bounce with 5.7.1 message rejected due to user rules
• Rejections cluster at one receiving provider or domain
• Delivery was fine and then degraded without a config change

Not for this skill when

• Mailgun returns API authentication errors (that is the API key, not delivery)
• The error is an unverified-domain rejection (that is identity setup)
• Messages are accepted but land in spam (reputation tuning, not rejection handling)

Variant phrasings

mailgun 5.7.1 rejected due to user rules

Short form. Same recipient-filter diagnosis.

mailgun bulk send rejected by recipient rules

Operator phrasing. Start with authentication, then reputation, then content.

user rules rejection mailgun bulk email

Search-shaped phrasing of the same bounce. Identical steps.

Why it happens

Receiving providers run rule engines over inbound mail, and aggressive or complaint-prone senders match more rules. Mailgun passes the rejection through verbatim, so the agent sees 'user rules' with no hint that the real cause is its own complaint rate, a listed IP, or content patterns the provider dislikes. Agents hit this when they scale volume before reputation is established.

Edge cases

• One recipient domain rejecting while others deliver is almost always that domain's policy, not your setup. Check that domain's postmaster guidance.
• Forwarded mail can inherit the forwarder's rules. Test with a direct address before concluding the content is the problem.
• A brand-new dedicated IP has no reputation; recipient filters treat it cautiously. Ramp volume gradually on fresh IPs.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_gnsna8QdSAGNh7xpw9wPcQ