What you want to do is a bulk add job which is described under
section 4.3 of the list owners manual (1.8c).

>     ADD listname DD=X IMPORT
>      //X DD *
>      address1 user name
>      address2 user name
>      addressN user name
>      /*

I created a new list and wanted to import all subscribers from one list
into the new list. The command works but adding addresses this way did not
send the welcome message of the new list to each added subscriber.

Any suggestions ?

Jacky