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Is there a guide/cheat sheet that explains Email/SMTP headers in detail? I could not find any useful resources after plenty of Googling.
The purpose is to understand the headers in order to be able to create advanced custom anti SPAM filters (not just based on common subjects and source IP addresses).
"Questions seeking product, service, or learning material recommendations are off-topic because they become outdated quickly and attract opinion-based answers. Instead, describe your situation and the specific problem you're trying to solve. Share your research." – Ƭᴇcʜιᴇ007 – 2014-04-13T14:44:02.080