How does Archive Manager process emails sent to distribution lists?
If journaling is not enabled, Exchange Store Manager would handle the message assignment.
When a message is found in the subfolder of the mailbox, the sql stored procedure assign security job would also assign these messages to the root of the mailbox.
If journaling is enabled, the dataloader would be able to expand the distribution list to get the individual recipients with envelope journaling.
Messages processed via the journal dataloader would have individual recipients and therefore could be associated via the assign security jobs.