Update golang.org/x/sync commit hash to 09787c9

See merge request !5

Update module chrj/smtpd to v0.2.0

See merge request !3

Update module jhillyerd/enmime to v0.8.3

See merge request !4

Update golang.org/x/sync commit hash to 67f06af

See merge request !2

Configure Renovate

See merge request !1

Run our own little SMTP server, attempt to parse all incoming
messages. Currently only DMARC email support is implemented (both ZIP
and gzip formats).

These originate from "report-uri" (not "report-to") tags in CSP
headers, and appear as application/csp-report requests.

It can be either a scalar or a list, skip parsing it for now as it is unused.

Also, stop logging the client IP for email reports, where it's just
going to be some email provider's reporting infrastructure.