A message containing a distribution list (DL) recipient is first routed to the designated DL expansion point if the DL has a Home-MTA (or locally if none is defined). If the message is routed locally, first a DL-expansion message copy is produced by fan-out, whose recipients are the DL members. This copy is passed back through the routing process. This process is repeated recursively for each nested level of the DL. The MTA verifies that an infinite loop is not generated by DL expansion.
Each MTA can also be configured to not expand replicated remote site DLs (use the MTA Site Configuration\General tab in the Administrator program).