use strict;
use warnings;

#Just listing a few bad chars (I think hehe) for example
my %escap_chars = ( '>' => '>',
                    '<' => '&lt;};

#Text for email would either be in array or scalar I'll presume
my $email_text = 'Hi this is a math email 2 + 2 = 4. and 4 > 5';
#if scalar
foreach my $key (keys(%escape_chars))
{
    $email_text =~ s/$key/$escape_chars{$key}/g;
}

# if each line of email is in an array

foreach my $key (keys(%escape_chars))
{
     s/$key/$escape_chars{$key}/g  for(@email_text);
}