Enable SMTP 8BITMIME for messages with 8-bit content:

Enable SMTP 8BITMIME for messages with 8-bit content:

1) In post, look for a Content-Transfer-Encoding header.  It has to
   be the header for the message, not any MIME parts.  If found,
   post trusts that it's correct.  If there isn't one, post scans
   the entire message body for any 8-bit bytes.

2) If the message body is 8-bit:
   If the server supports 8BITMIME, enable it.

   If the server doesn't support 8BITMIME, fail with a message to
   user that they need to encode the message for 7-bit transport.