-report-mail option does not output required mail header

[hogehuga]

-report-mail option outputs the following headers.

• To: <to_address>
• Cc: <cc_address>
• Subject:
• Context-Type: text/plain; charset=utf-8

RFC required "Date" and "From" header.

• https://www.ietf.org/rfc/rfc2822.txt
  • "3.6. Field definitions" says..
  • "The only required header fields are the origination date field and the originator address field(s). "

We need "Date" header.