One may always refer to a list by its object number. In order to refer to it by name, it must be contained in $mail_agent, which holds all mailing lists, i.e., those that you want others to be able to refer to by name.
The .aliases field holds the names by which one may refer to the list, but only those names not containing spaces actually count for anything. As with certain other types of objects (e.g., players), set_aliases() needs to be called in order to change the .aliases field.
$mail_agent:match(name)
is the canonical way to obtain the objectid of a mailing list
given the name ("*" is assumed; an initial "*" will be dropped).
$mail_agent:match_recipient(name)
is the canonical way to obtain the objectid of a list or player
matching the given name. An initial "*" indicates that this is
supposed to be a list.
$mail_agent:match_failed(objid,name)
is the mail_recipient counterpart to $command_utils:object_match_failed