Problem on SMTP: 554 5.6.0 Message contains invalid header.

Hello, thanks for the great job. After a lot of testing I finally managed to get the code running correctly on Arduino with shield W5100. (smtp.orange.fr) The mails are sent correctly. I received the email on my ztu.gmail.com mailbox but when trying to receive it on an xyz@wanadoo.fr address I received an email on my sending mailbox: host back1g-mail01-041.me-wanadoo.n<wbr />et [10.232.119.68] said: 554 5.6.0 Message contains invalid header. After a lot of research (not very successful) I found this: 1) It is absolutely necessary to put an empty line between the subject and the body of the message! Anyone know how to do this? 2) Put the recipient first ... Or in any case solve my problem of shipping email to an orange.fr address Thank you