/etc/zarafa/spooler.cfg:

archive_on_send = yes

This causes zarafa-spooler to archive each message it sends if the primary store from which the message is send is attached to an archive. If the archive operation fails zarafa-spooler won’t send the message and creates a bounce message for the sender.

Sent messages are archived in a special folder in the users archive: Zarafa Archive/Outgoing. These messages are not coupled to the copies of the sent messages that can be found in the user’s Sent Items folder. This implies that sent messages are archived twice.