...

recipient_delimiter = +

transport_maps =
   btree:/etc/postfix/transport
   btree:/etc/postfix/relay_domains
   regexp:/etc/postfix/sympa_transport

...

sympa_destination_recipient_limit = 1

sympabounce_destination_recipient_limit = 1

...

relay_domains =
   $mydestination
   btree:/etc/postfix/relay_domains
   btree:/etc/postfix/sympa_domains

...

virtual_alias_maps =
   regexp:/etc/postfix/sympa_virtual_aliases
   ## - mailman
   #hash:/var/lib/mailman/data/virtual-mailman