you can't use a here document like that send_mail($email_400, <<EOF ); because there's a right bracket and semicolon introduced as part of the here document or the start here document marker. either result is undesirable. A here document start marker needs a semicolon directly after the here document name (EOF in this case) afaik. one possible way is 
if($email_400) {
  my $email_content = <<EOF;
To: $email_400
..
..
EOF
  send_mail($email_400,$email_content);
}

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the hardest line to type correctly is: stty erase ^H

In reply to Re: uninitialized value in concatenation by aquarium
in thread uninitialized value in concatenation by Galceran

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