Subject: RFC 8621 Section 4.1.4 test Content-Type: multipart/mixed; boundary="1" --1 Content-Type: text/plain Content-Disposition: inline A --1 Content-Type: multipart/mixed; boundary="2" --2 Content-Type: multipart/alternative; boundary="3" --3 Content-Type: multipart/mixed; boundary="4" --4 Content-Type: text/plain Content-Disposition: inline B --4 Content-Type: image/jpeg Content-Disposition: inline C --4 Content-Type: text/plain Content-Disposition: inline D --4-- --3 Content-Type: multipart/related; boundary="5" --5 Content-Type: text/html E --5 Content-Type: image/jpeg F --5-- --3-- --2 Content-Type: image/jpeg Content-Disposition: attachment G --2 Content-Type: application/x-excel H --2 Content-Type: message/rfc822 Subject: J J --2-- --1 Content-Type: text/plain Content-Disposition: inline K --1--