It sounds to me like you should keep binmode on at all time, so no automatic conversion, and convert "\n" to "\015\012" only in the headers, by hand. AFAIK, constantly swapping between binmode and text mode for a handle doesn't work well.

Note that 

substr($string, $start, $length) =~ s/\n/\015\012/g;

[download]
should work fine. You only still have to locate the offsets/lengths of the substrings containing the headers.

In reply to Re: Creating MIME entities with CRLF line endings by bart
in thread Creating MIME entities with CRLF line endings by sgifford

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