Action mailer 'Content-Type' found without required MIME hea

In my application i use the actionmailer.
When i send a message to myself my spamfilter noticed the following
error

MIME_HEADER_CTYPE_ONLY ‘Content-Type’ found without required MIME
headers
AND
MIME_HTML_NO_CHARSET RAW: Message text in HTML without charset

Is there a way to fix this?

Thanks in advance