send html with perl MIME:Lite

Today I encounter a problem when sending html content via Perl's MIME:Lite, in my html there is always a </tr> got broken...damn it!

 

I checked the html string, it's all right. Finally I found there is a config for MIME:Lite:

 Use encoding:     | If your message contains:
   ------------------------------------------------------------
   7bit              | Only 7-bit text, all lines <1000 characters
   8bit              | 8-bit text, all lines <1000 characters
   quoted-printable  | 8-bit text or long lines (more reliable than "8bit")
   base64            | Largely non-textual data: a GIF, a tar file, etc.

I noticed that my html is a single line document and with size > 1000!!!, After I add some \n to the content, all is OKay!