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Grey List
Greylisting is a method of defending e-mail users against spam. A mail transfer agent (MTA) using greylisting will "temporarily reject" any email from a sender it does not recognize. If the mail is legitimate, the originating server will try again after a delay, and if sufficient time has elapsed, the email will be accepted. How it works A server employing greylisting temporarily rejects email from unknown or suspicious sources by sending 4xx reply codes ("please call back later"), as defined in the Simple Mail Transfer Protocol (SMTP). Fully capable SMTP implementations are expected to maintain queues for retrying message transmissions in such cases, and so while legitimate mail may be delayed, it should still get through. The temporary rejection can be issued at different stages of the SMTP dialogue, allowing an implementation to store more or less data about the incoming message. The trade-off is more work and bandwidth for more exact matching of retries with original message ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
E-mail
Electronic mail (email or e-mail) is a method of exchanging messages ("mail") between people using electronic devices. Email was thus conceived as the electronic ( digital) version of, or counterpart to, mail, at a time when "mail" meant only physical mail (hence '' e- + mail''). Email later became a ubiquitous (very widely used) communication medium, to the point that in current use, an email address is often treated as a basic and necessary part of many processes in business, commerce, government, education, entertainment, and other spheres of daily life in most countries. ''Email'' is the medium, and each message sent therewith is also called an ''email.'' The term is a mass noun. Email operates across computer networks, primarily the Internet, and also local area networks. Today's email systems are based on a store-and-forward model. Email servers accept, forward, deliver, and store messages. Neither the users nor their computers are required to be online simult ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
