I'm not sure why, but I have a couple of comments anyway. Why do you use quotes around something that is a string anyway? i.e.: $hash_ref->{"$meta_configs{login_username}"}; looks better as $hash_ref->{$meta_configs{login_username}}; and $dbh->prepare("$sql") makes more sense as $dbh->prepare($sql)

Also, you could consider using a module such as Mail::Sendmail which means your code is a lot more portable, especially on systems where /usr/lib/sendmail doesn't exist, which I assume will be plentiful. It also should fix the problem with taint.

Also why the convulted way to get the username and password, whats wrong with:

my ($email, $user, $pass) = $sth->fetchrow_array;
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