MAC, Media Access Control, address is a globally unique identifier assigned to network devices, and therefore it is often referred to as hardware or physical address. MAC addresses are 6-byte (48-bits) in length, and are written in MM:MM:MM:SS:SS:SS format. The first 3-bytes are the ID number of the manufacturer, which is assigned by an Internet standards body. The second 3-bytes are serial numbers assigned by the manufacturer.

address and the host address. A subnet mask separates the IP address into the network and host addresses (<network><host>). Subnetting further divides the host part of an IP address into a subnet and host address (<network><subnet><host>) if additional subnetwork is needed. Use the Subnet Calculator to retrieve subnetwork information from the IP address and Subnet Mask. It is called a subnet mask because it is used to identify the network address of an IP address by performing a bitwise AND operation on the netmask.

The Internet Protocol Address (or IP Address) is a unique address that computing devices such as personal computers, tablets, and smartphones use to identify themselves and communicate with other devices in the IP network. Any device connected to the IP network must have a unique IP address within the network.

With ever growing number of spam emails flooding the Internet, more and more ISPs tighten their email filtering system to prevent spams delivered to their clients. It is virtually impossible to block even 50% of the spams arriving in a mail server, and there will always be false positives (legitimate emails filtered as spams). In an effort to reduce spam emails, the Federal Trade Commision (FTC) passed the CAN-SPAM Act of 2003, but the Internet spam traffic is still on the rise.