Support viewing full SMTP protocol conversation

[Vasco-jofra]

Please describe your feature request:

Ability to read the full SMTP protocol conversation instead of just the email contents.

Describe the use case of this feature:

Useful to test email-related vulnerabilities such as those described in https://portswigger.net/research/splitting-the-email-atom . Burp's collaborator has this feature.

Implementation

I made a commit at Vasco-jofra@11b8c75 that supports this using the smtpd library's LogRead/LogWrite callbacks; however, these are prone to race conditions if two requests come in from the same IP at the same time. I'm also storing it in the RawResponse, which may not be ideal.

I wanted to know if you have any feedback on this approach and how we could improve its implementation.