in reply to why is this tainted?
The error message doesn't say $email is tainted. $ENV{PATH} is. You must do something like $ENV{PATH} = '' to fix this, and then (as you are correctly doing) rely on providing the full path to your external applications in your script.
Also, $email, coming from an external source (the database) *should* be considered tainted (and once you fix the PATH variable, you may get a message for $email). It is tainted because it was not provided by your script, nor was it "cleaned" by your script. If someone can put a harmful string into your database, they've just fouled up your pipe. You will want to verify that $email is a conformant email address before sending it to sendmail.
All that said, I would strongly advise against using this sort of pipe to sendmail in a taint protected CGI. You might want to take a look at the various email modules on CPAN, especially Mail::Sendmail.
Also, $email, coming from an external source (the database) *should* be considered tainted (and once you fix the PATH variable, you may get a message for $email). It is tainted because it was not provided by your script, nor was it "cleaned" by your script. If someone can put a harmful string into your database, they've just fouled up your pipe. You will want to verify that $email is a conformant email address before sending it to sendmail.
All that said, I would strongly advise against using this sort of pipe to sendmail in a taint protected CGI. You might want to take a look at the various email modules on CPAN, especially Mail::Sendmail.
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