Well, you could just dump the usernames into state buckets and then retrieve them by state:

use strict;
use warnings;

my (%hash, %states);

while (<DATA>) {
    chomp;
    @_ = split /: /, $_, 2;
    $hash{$_[0]} = $_[1];
}

for (keys %hash) {
    push @{$states{(split /:/, $hash{$_})[1]}}, $_;
}
for (sort keys %states) {
    print $hash{$_}, "\n" for @{$states{$_}};
}

__DATA__
alpha: 12:NY:me@yoiu.com
beta: 13:MO:fg@yoiu.com
gamma: 14:DE:fghh@yoiu.com
delta: 15:MO:adf@yoiu.com
epsilon: 16:DE:mjhg@yoiu.com
iota: 17:NY:juyu@yoiu.com
eta: 18:NY:mjhk@yoiu.com
[download]

The transform method is so much neater, though.