| 摘要 |
<p>Email filter for blocking spam and other unwanted mail only delivers messages from approved addresses. Addresses can be approved manually by the receiver or using a 'personal identifier'. The personal identifier can be included in the email address/subject lines and the filter checks for its presence in all mail from unapproved addresses. Alternatively email from unapproved addresses are directed to a web site to enter the personal identifier. The personal identifier can be a secret communicated to the sender, or it could be a CAPTCHA in the form of obfuscated text or question to be answered. If the personal identifier is proved the email is delivered and the sender address added to the approved list, otherwise the email is dropped by the server.</p> |
