Regarding SMTP Message specification syntax ...

Hi,
    If user enters "." or "CR" as a first character for a response to DATA
command. Then, should that be treated as illegal message format ?
    I went through RFC822 in search of this, but could not gain much from
"Message specification section 4.1" with regards to this issue.
    It would be really great, if I can get some pointers to resolve this
issue.

Regards,
Dhananjay.