=== The local network===
Whether you are connecting to the Internet from home, office, Internet cafe or another location, the first point of call for your email on its way to the recipient is the local modem – the one which is connected to the Internet. Whoever has access to this modem will be able to view the network's traffic as it is sent and received from the Internet.
Note: Open wireless networks (those that do not require a password to connect) are just as vulnerable to surveillance by anyone connected to the same wireless router. They present an even greater risk since anyone within range can connect. Wireless networks protected by a password present a much greater challenge, since everyone's connection to the router is encrypted with an individual session key. You should be using a long WPA2 standard password (as opposed to a WEP key) and if your router doesn't have that option – time to upgrade!
===The Internet Service Provider===
The local ISP plays the role of a postman for your Internet connection. He delivers and collects all of your communications with the Internet. He assigns your computer its IP address and can keep a log of your online activities (often by law). The ISP manages and has access to the traffic data of all its clients. Internet surveillance and censorship is often implemented at the ISP level. In many countries users are offered a choice between different ISPs and should consider the company's privacy and data retention policies when doing so.
===The National Gateway===
Every country needs to manage its entry and exit points to the Internet. Usually this is done by large telecommunications providers operating according to national legislation. Sometimes these gateways are run and managed by the ministry of communications directly. These gateways have access to national traffic data and some countries implement Internet surveillance and censorship at this level.
Modern Internet surveillance (or monitoring) is done by software looking for specific keywords or phrases. This is known as flagging. Whenever a particular keyword passes through the infrastructure, the IP address of the sender is recorded along with the message. Flagging could also react to requests for certain websites. In a targeted surveillance scenario, a particular IP could be singled out for monitoring and all of its activity recorded.