$__to =~ s/(\r\n|\n\r|\r|\n)/\r\n/sg;
    $__cc =~ s/(\r\n|\n\r|\r|\n)/\r\n/sg;
    $__bcc =~ s/(\r\n|\n\r|\r|\n)/\r\n/sg;
    $__from =~ s/(\r\n|\n\r|\r|\n)/\r\n/sg;
    $__subject =~ s/(\r\n|\n\r|\r|\n)/\r\n/sg;
    $__html_message =~ s/(\r\n|\n\r|\r|\n)/\r\n/sg;
    $__text_message =~ s/(\r\n|\n\r|\r|\n)/\r\n/sg;
    $__importance =~ s/(\r\n|\n\r|\r|\n)/\r\n/sg;
    $__xpriority =~ s/(\r\n|\n\r|\r|\n)/\r\n/sg;
    $__x_ms_priority =~ s/(\r\n|\n\r|\r|\n)/\r\n/sg;
    $_mail_Message =~ s/(\r\n|\n\r|\r|\n)/\r\n/sg;
[download]

I personally believe that if those substitutions are in fact all the same substitution, which seems to be the case -and would be most reasonable/probable- although I'm not sure due the alignment... then I should point out, on a totally OT basis wrt your actual problem, that you'd probably better do:

s{ \n\r | \r | \n }{\r\n}gx for
    $__to,
    $__cc,
    $__bcc,
    $__from,
    $__subject,
    $__html_message,
    $__text_message,
    $__importance,
    $__xpriority,
    $__x_ms_priority,
    $_mail_Message;
[download]

I also edited the regex to the point of:

• removing a set of unnecessary capturing parens;
• removing a pattern that would be replaced by itself;
• improving readability with /x (incidentally, /s did nothing there...) and alternate delimiters.