Email blocking: are your SPF, DKIM and DMARC controls keeping up?

TL;DR: Emails get blocked or routed to spam when SPF, DKIM, DMARC, reputation, content signals, or account compromise undermine deliverability, according to EasyDMARC’s guide. The control problem is not just delivery noise: authentication, sender trust, and compromise response have to be governed together, or legitimate mail will fail for predictable reasons.

Editorial analysis by NHI Mgmt Group, based on content published by EasyDMARC: “Why Are My Emails Being Blocked? Causes & How to Fix It”.

Key questions

Q: What should security teams do first when legitimate email starts getting blocked?

A: Start with the sender inventory, not the symptom.

Q: Why do authenticated emails still end up in spam or get blocked?

A: Authentication proves origin, but it does not override mailbox policy.

Q: What breaks when SMTP credentials or API keys are abused for email sending?

A: The trusted mail path becomes contaminated.

Practitioner guidance

• Map every authorised sending source Document each platform, application, and service that can send mail for the domain, then verify it is represented in SPF, DKIM, and DMARC alignment.
• Review account and SMTP abuse paths Check for unknown forwarding rules, unfamiliar users, exposed SMTP credentials, and suspicious API keys that could be sending through trusted infrastructure.
• Tighten DMARC only after inventorying senders Move to stricter policy only when legitimate email streams are fully known, tested, and passing alignment, so business mail is not rejected by design.

Bottom line: Email blocking usually starts with broken trust signals, not with the content of a specific message.

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