Email security by Pablos Holman in 2002 (still relevant in 2023)
https://www.youtube.com/watch?v=th5HRiNKTYw
https://www.blackhat.com/presentations/bh-usa-02/bh-us-02-holman-email.pdf
Point of view on open ecosystem by Signal founder:
https://signal.org/blog/the-ecosystem-is-moving/
Microsoft Patent for enhanced email service
https://patents.justia.com/patent/20200099695
Other patents to read: 11665177, 10992650, 10887261, 10855635, 10701100
https://www.mimecast.com/state-of-email-security/
https://www.fortra.com/blog/untrustworthy-email-inboxes-reaches-all-time-high
https://www.bankinfosecurity.com/whitepapers/state-email-security-2022-confronting-new-wave-cyberattacks-w-10165
https://cofense.com/annualreport/
https://www.barracuda.com/reports/email-security-trends-report-2023
https://dmarcreport.com/blog/an-overview-of-email-security-landscape-in-2023/