On Monday, Yahoo! Mail took a step toward e-mail authentication, considered a spam-fighting technique, by encrypting a Yahoo! signature on most outgoing Yahoo! mail, and also scanning incoming
messages for the signature. Most customers are not likely to notice the change, unless they are particularly computer-savvy and search out the details about the e-mail's path to their inboxes, said
a Yahoo! spokeswoman. The company is in discussions with other Internet service providers to share information about its signature program, so that other ISPs could have the option of blocking e-mail
lacking the signature.