CollabNet TeamForge discussions provide workspaces where project members can work together online or by email.
Discussion forums and mailing lists are closely integrated. Forum administrators can choose to enable a mailing list for each project forum. A mailing list extends the discussion forum functionality to allow project members to post messages to the forum using email.
In a moderated discussion, messages from anyone except "trusted" users are screened by a moderator before they are posted. Messages posted by trusted users do not require the moderator's approval.
It's a good idea to use a discussion forum instead of direct personal email whenever privacy or security concerns don't prevent it, even when the communication only involves two project members.