Figure out envelope-from and response-path

[Paul Everitt]

As discussed in email, we need to find out why setting envelope_from_addr in karl.ini doesn't actually generate a return-path which allegedly then sets envelope-from in the SMTP handshake.

This is likely to involve a lot of research. Looking at the KARL code, I'm not really sure where I see return-path getting set, much less envelope-from.

- KARL emails get a bad spam score at OSF because we don’t send an envelope-from during the SMTP handshake

- That handshake usually (I *think*) reads the value from the RFC822 “Return-path” header if the SMTP handshake doesn’t provide it

- We actually confronted this in 2011:

  https://bugs.launchpad.net/karl3/+bug/785267

- src/karl/CHANGES.txt says:

  3.60 (2011-05-20)
  -----------------

  - Refactored outgoing email to use Karl configuration for the envelope from
  address. (LP #785267)

In the LP ticket, Chris says it defaults to karl@system_default_email_domain. But it doesn’t appear to be defaulting to anything. I don’t know if we have to figure out whether the SMTP handshake has envelope-from or also ensure our emails don’t have response-path: <>