Evaluate the rendered message
Content checks should use the final sent MIME output after the ESP has rewritten links, injected tracking, added footers, and assembled text and HTML parts. Draft copy is not enough evidence.
Content
Content & headers
SpamAssassin rules, plain-text vs HTML, trigger words and the headers receivers actually read.
How to use this topic
Start with the pillar guide for the full model, follow the diagnostic workflow for the current problem, and use the commercial destination when the evidence needs to become a repeatable team process.
Test the complete messageEvaluate the final MIME message instead of relying on generic trigger-word or image-ratio rules.
Curated guide
Avoid one-rule content myths
Image ratio, spam phrases, and formatting choices can contribute risk, but they are not universal pass-or-fail rules. Interpret them beside authentication, reputation, links, and recipient context.
Check headers receivers care about
Required fields, valid dates, unsubscribe headers, MIME boundaries, and safe link structure make the message easier to parse and debug. Header quality also improves investigation when something changes.
Diagnostic workflow
- Step 1
Inspect structure
Check headers, MIME alternatives, unsubscribe support, links, and message size.
Open workflow - Step 2
Interpret content signals
Use evidence from the full message instead of treating one heuristic as a universal rule.
Open workflow - Step 3
Retest the rendered send
Run the final version after the ESP has rewritten links and injected required footers.
Open workflow
Relevant free tools
- Header analyzer
Inspect required fields, MIME, dates, unsubscribe support, and risk signals.
- Free tools hub
Use DNS and authentication diagnostics alongside message analysis.
Supporting guides
- ·3 min read
Email image-to-text ratio: myth, evidence, and testing
There is no universal image-to-text cutoff. Learn what image-heavy email can break, which signals matter, and how to test the final MIME message.
Read - ·2 min read
Accessible HTML email: structure, contrast, and testing
Create accessible email with semantic structure, readable contrast, useful alternative text, and production-like client testing.
Read - ·3 min read
Plain text vs HTML email: why both matter
Why HTML-only emails get filtered, what a clean multipart/alternative looks like, and the four-line MIME structure to copy.
Read - ·3 min read
Email spam trigger words: what SpamAssassin actually scores
See why isolated words rarely decide placement, which structural and phrase combinations score, and how to test the final message.
Read
Frequently asked questions
- Do spam trigger words automatically send email to spam?
- No. Content contributes signals, but authentication, reputation, list quality, links, and recipient behavior are also important.
- Should an HTML email include a plain-text part?
- Yes. A meaningful multipart alternative improves compatibility, accessibility, and diagnostic clarity.