I tried to look on various forums and everywhere i get advice using MIME :: Lite. Unfortunately i cannot use it.

Care to tell why? Since you are able to use MIME::Base64 and MIME::QuotedPrint it should not be too difficult to include a use MIME::Lite in there.

If you get the advice to use MIME::Lite everywhere, why should that be different here?

please help me in debugging above code.

Please go over your post again and enclose the above code within <code> tags. If you want help, help us to help by making your posting readable. See Writeup Formatting Tips for details, and use the preview button.

That said, there are several errors (uncomplete list):

• you use the hash %mail, but later you try to access the value stored under the key 'body' as a reference - $$mail{body}
• you try to add a string to an empty hash value.
  Wrong:

  $mail{body} += encode_base64(<IN>); # addition won't work
  [download]

  That should be:

  $mail{body} = encode_base64(<IN>); # just assign it
  [download]

  or if you want to append:

  $mail{body} .= encode_base64(<IN>); # just assign it
  [download]

  See perlop.
• mismatch between here-document delimiter introduction and actual delimiter:

  $mail{body} = <<EOD; <--- delimiter
  ...
  $mail{body}
  --$boundary
  Content-Type: application/vnd.ms-excel; name="$file3"
  Content-Disposition: attachment; filename="$file3"
  Content-Transfer-Encoding: base64
  Content-Length: $len
  
  $mail{body}
  $boundary--
  END_OF_BODY          <-- wrong delimiter
  [download]

• in the above snippet, you include the same chunk of data twice: $mail{body}. Do you expect different attachments? Then use different data.
• what content does $message have?

Fix that, and add use strict; use warnings; at the top of your script! That will make perl tell you about blatant errors, so we don't have to.

_($_=" "x(1<<5)."?\n".q·/)Oo.  G°\        /
                              /\_¯/(q    /
----------------------------  \__(m.====·.(_("always off the crowd"))."·
");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}