Key points
- Missing SPF/DKIM/DMARC is the #1 cause
- Spammy content patterns trigger filters
- Low sender reputation hurts
- Authentication fixes most cases within days
How to do it
- Authenticate your domain (SPF/DKIM/DMARC)
- Check your content for spam triggers
- Clean your list
- Warm up a new domain gradually
- Monitor reputation
Common mistakes
- No authentication
- Buying lists
- Sending image-only or all-caps emails
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