headers_end = __build_address_headers(options)
headers_end += 'Message-Id: %s\n' % msg_id
+ if options.refid:
+ headers_end += "In-Reply-To: %s\n" % options.refid
+ headers_end += "References: %s\n" % options.refid
if options.version:
version_str = ' %s' % options.version