No e-mails to Hotmail/t-online/ possible

Hello,
i am new here
and i have a problem with Send e-mails to Hotmail or t-online


i get this error message from Hotmail

Undelivered Mail Returned to Sender
This is the mail system at host

I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.

For further assistance, please send mail to postmaster.


And from t-online
they do not receive e -mails
when i send a e-mail the user dont get the e-mail

can you help me?

Thanks