[PHP] Append a line to a text file

[Rodrigo]

I need to add a email to the text file that is already written, but I
get the file writen over , so I always get only the last email send by
the form.
 
What I need is a form that get the e-mail and it writes the email at the
end of a text file.
 
Thanx,
 
Rodrigo