In order to allow handlers to manipulate with the current user data we could introduce user context switching.
By default, the "current" user should be an Anonymous user. Each analyzer could update it with their (user) findings.
UserAnalyzer could be implemented to extract the mail address from "From" mail header field and find a corresponding user in the system. Thus, the user context could be updated.
Mailhandler currently supports PGP-signed emails which could allow
PGPAnalyzer to update user context as well.