I am working on an article explaining aspects of message verification such as SPF, DKIM, DMARC and ARC. I have been studying how messages are marked as spam. I have observed that some messages that would be purely legit (like from my bank) are occasionally marked spam. Others show inconsistency -- such as my articles from Substack being marked as spam for some addresses I own, while others are not. I am particularly interested in how Thunderbird is interpreting the header in regards to source verification. In most of my articles I have advocated for a scoring system that would better inform the recipient of the trustworthiness of the message. I noticed there is an X-spam tag on some messages that is based on a scoring algorithm. Appreciate your assistance. Eric