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Internet and Data Security Knowledgebase

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NAT Network Address Translation (NAT) typically has the effect of preventing connections from being established inbound into a computer, whilst permitting connections out.
For a small home network, software NAT can be used on the computer with the Internet connection, providing similar behaviour to a router and similar levels of security, but for a lower cost and lower complexity.
NDR A non-delivery report or NDR is a DSN message sent by the email server (mail transfer agent or MTA for short) that informs the sender that the delivery of the email message failed.
While there are various events that can trigger an NDR, the most common cases are when the recipient of the message does not exist or when the destination mailbox is full.
NDR Spam A spammer often uses a faked sender address. If this address belongs to a valid user then this user ends up receiving the non-delivery reports.
Since the emails sent out by the spammer tend to be in large numbers, thousands of NDRs may end up in the victim's mailbox. The resulting emails are known as NDR spam or backscatter.
Non-repudiation A method of transmitting information (typically email) where the sender gets proof of delivery and the recipient is certain of the identity of the sender so that neither can later deny having processed the information.

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