If you type in all the addresses on one line, even as a csv list, what you'll get is all the input addresses as the first element of the @addresses array.
This is not going to work. You need to

(@addresses) = split(/,/ $usermail);

and enter them as a csv list on the cmd line.

Otherwise, loop around the push(), entering each addr on a new line, until you've done them all, then proceed.