I suspect a lot of the problem has to do with how you sign it, and how Yahoo Groups deals with attachments. When you simply use the BEGIN PGP... header/footer, it's all text, so when Yahoo adds it's ad to the text, it does so after the signed text. When you sign a MIME attachment, it either strips off the signature, or it adds to the text/plain portion of the message, which means it won't validate. Bob