The .+ is greedy by default. Non-greedy: .+?. Do you really have a space char at the beginning of the line? Why do you include spaces in your search pattern?

    $_ =~ s/(.+?\@)(.+?\.)(.+?)/$1something.$3/g;
[download]

Without captures, using look-behind and look-ahead:

    $_ =~ s/(?<=\@).+?(?=\.)/something/g;
[download]

See perlre.

--shmem

_($_=" "x(1<<5)."?\n".q·/)Oo.  G°\        /
                              /\_¯/(q    /
----------------------------  \__(m.====·.(_("always off the crowd"))."·
");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}