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Here are some quick wins to lower your spam score

Create a text version.
Avoid usage of spam-sensitive words and phrases.
Use normal text inside hyperlinks, instead of the URL.
Use a proper from address.
Use a proper subject line.
Avoid HTML errors, unsupported techniques, obscure content, obfuscation.
Images.
HTML.

SEO Copywriting: 9 Tips for Using Keywords in a Natural Way

For SEO Writing, Do Start with the Keywords.
Write for Your Audience, not Your SEO.
Mix It Up When Using Keyword Phrases.
Focus on Your Headline.
For SEO Writing, Go for Length.
Keep Keyword Density in Check.
Go Easy on Your Anchor Text.