Type: boolean
Default: unset
Warning: do not set this variable unless you are using a version of
sendmail which supports the -B8BITMIME
flag (such as sendmail 8.8.x) or
you may not be able to send mail.
When set, Mutt will invoke
$sendmail
with the -B8BITMIME
flag when sending 8-bit messages to enable ESMTP
negotiation.