Rails - Jun 2011 - ActionMailer Problem

Hi,
I wanted to send an attachment in mail.
for testing , I have send png image attachement in mail. Mail delivery is
completely working but the attachment in that mail show file name as
"nonname"
what should i do??
My code is:

class SendMail < ActionMailer::Base
  default :from => "XXXX-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org"

  def welcome
    attachments["adfd.txt"] =
File.read("#{Rails.root}/public/images/f.txt")

     mail(:to => "XXX-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org",
          :subject => "welcome mail").deliver
  end


end

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