The mail exchange (MX) resource record specifies a mail exchange server for a DNS domain name. A mail exchange server is a host that will either process or forward mail for the DNS domain name. Processing the mail means either delivering it to the addressee or passing it to a different type of mail transport. Forwarding the mail means sending it to its final destination server, sending it using Simple Mail Transfer Protocol (SMTP) to another mail exchange server that is closer to the final destination, or queuing it for a specified amount of time.
There are several ways to classify natural resources, including where they come from and if they are renewable or not. If natural resources come from living things or organic materials, then they are considered biotic resources . Biotic resources include plants, animals, and fossil fuels. The three fossil fuels are coal, oil, and natural gas. Fossil fuels are classified as biotic resources because they were formed from the decay of organic matter over millions of years. On the other hand, abiotic resources originate from nonliving and inorganic materials. For example, air, sunlight, and water are abiotic natural resources. Minerals (gold, copper, iron, diamonds) are also considered abiotic.