3.4.6 Redmine doesn't support ruby-mail beyond 2.6.4. Neither does the latest 3.4.x release.
This package would need to be updated to Redmine 4.0.1 and track the 4.0.x series to get the proper ruby-mail support. (Looking into this downstream in Ubuntu, this was discovered. I am simply sharing this information for the purposes of making sure this bit is known here)
