use strict;
use warnings;

my $addr = q{xqwertyxyx@gmail.com};

my ( $name ) = $addr =~ m{^([^@]+)};
my %letterFreq;
$letterFreq{ $_ } ++ for split m{}, $name;

print
   map  { qq{$_: $letterFreq{ $_ }\n} }
   sort { $letterFreq{ $b } <=> $letterFreq{ $a } || $a cmp $b }
   keys %letterFreq;