This article is for Redmine admins.

1. Go Administration page
2. Go group page
3. Add them to ruby-core group

Login neon (or something; see header of the mail)

LC_ALL=C sudo -u list /usr/lib/mailman/bin/remove_members ruby-core <address>

Instead of removing the account, you should lock it. It makes easy to recover and remove all comments related the account.

search the user and lock them.