Currently, the techconduct@ address is configured to only allow group members to send mail (thanks André for the report).
This mail is intended to allow all users (including users external to the wikimedia.org organization) to write when they find a violation of the code of conduct. It's published at https://www.mediawiki.org/wiki/Code_of_Conduct as the point of contact to report problems, and this link is published to all our repositories.
This mail is managed at G Suite (formerly Google Apps) level.
Could you reconfigure it?