... Using PGP or similar to make an encrypted file (txt or word or something). Then attach it to an ordinary webmail upload function, to send it over to the recipient that alreday are informed of my public key (and who´s key I have). All this whitout any need for Thunderbird or anything in computer.
something like freenigma? http://www.freenigma.com/
you have to trust them with your keys, but at least provides some protection for the scenario you describe.