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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