Under strict you must declare every variable you use, scalar, array, hash doesn't matter.
my @email = ""; is plain wrong, because @mail is an array and "" is a scalar.

I suspect one of your misunderstandings is what 'value' a not explicitly defined variable has.
Scalars are simply undefined; arrays and hashes are just empty.

my @array;  # emtpy array
my @array = (); # empty array

my %hash; # empty hash
my %hash = (); # empty hash (not sure about this *blush*)

my $scalar; # undefined scalar
my $scalar = ""; # scalar with empty string as value
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You do have to do the same with arrays. Hashes, too.

---
print map { my ($m)=1<<hex($_)&11?' ':'';
$m.=substr('AHJPacehklnorstu',hex($_),1) }
split //,'2fde0abe76c36c914586c';
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I am very suprised that you have never seen a script that uses my to scope an array. It is used to scope a variable to enclosing brackets (or Main if there are no enclosing brackets).

Consider the following VERY contrived example:

#!/usr/bin/perl -w
use strict;
my @array;  # no enclosing braces - scoped to Main
my $var1 = 3;
my $var2 = 4;
foreach (1..10) {
   push @array , $_;
}
if ($var2 > $var1) {
   my @array = ($var1 , $var2);
   print "$_\n" foreach (@array);
}
print "Other array\n";
print "$_\n" foreach (@array);
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This allows you to use the same variable name numerous times within the same program without stepping on each other. It should not be confused with local, which I will leave you to read the Perl docs to grok.

Cheers - L~R

Using my you're scoping your variables.