This EXPERIMENTAL patch has a basic implementation of MTA-STS (Strict
Transport Security), based on the current draft at
https://tools.ietf.org/html/draft-ietf-uta-mta-sts-02.
It integrates the policy fetching and checking into the smtp-check tool
for convenience, but not yet in chasquid itself.
This is a proof of concept. Many features and tests are missing; in
particular, there is no caching at all yet.
This patch is the result of running go vet, go fmt -s and the linter,
and fixing some of the things they noted/suggested.
There shouldn't be any significant logic changes, it's mostly
readability improvements.
This patch adds a small utility called "smtp-check" that will perform basic
checks on the SMTP setup for the given domain.
Only basic things are implemented for now.
