127.0.0.1 Ip Loopback

For you Networking guru's I beg forgivness in taking liberty with definitions and this is not designed to be a exact explanation but a fast, general and broad one. Now with that said:

In the world of Networking everything that can get an address gets an address.

This is to make the Machine unique from other machines that are interconnected local and worldwide. Machines get an ip number from the internet provider before going out on to the internet. Machines can get a ip number from a router or other networking device to make it unique on a local network. You can even assign a ip number yourself to make a device unique. Some ip addresses are written into software and make changes to which ip addresses a machine will use. All of this is done to have a local machine be able to talk to a remote machine. A list of these addresses (sometimes called a table) is stored on these devices that they are given, learned or knows. The Machine will use these address to identify its self and to communicate to others.


There are some addresses that a machine has been given, learned, or knows that have special purposes.

127.0.0.1 being one of them. You may know it by the name "localhost". On your computer this address is already in a table or list of known addresses.
So what is does this special address do? Several uses actually, different applications and programs will use this special address to perform special functions.

One special function is for testing your network interface ability to send and receive traffic.

Being able to communicate with one's local machine as though it were a remote machine is useful for the purposes of testing. Comunications being sent out from a computer to the address 127.0.0.1 is essentially sending a message to itself. This is why it is called a loopback address. It goes nowhere but to itself. This testing can be automated or manualy done. A good way to think of this address as THIS MACHINE.

Another special function is anti-virus/malware scanning of emails.

If you have selected in your anti-virus/malware application to scan incomming email, it will grab/divert this incomming email first rather than the Email application getting it. Then sends it back out using the 127.0.01 loopback address as source address of the Email and then the Email application will recieve/display it.

This is where you may be seing the 127.0.0.1 address for incoming emails. It literally made a trip through your machine as receiver and re-sender of the Email. Remember everything gets an address? One computer sending something to a remote computer.

There are other special uses for the 127.0.0.1 address, but I leave that up to you to discover.

Regards
Kaz.

Thanks Kaz. for the informative explanation. I think the Networking guru's would be proud! My concern is that most of my emails have this in the header. I do not use an email client, my isp is earthlink and I use their webmail program, therefore, none of my emails, in or out, are actually on my computer. Can I post email headers here? Would you or anyone else be able to tell me if something is weird or wrong? Thanks again!

Please feel free to do so, but I am still betting on your antivirus/malware application doing this to email no matter where it comes from. Wouldnt be much of a email scanner if it only scanned SMTP mail only. The other possibility is that it is being scanned/filtered before you get it by the "holder" of the email. Lots of online/webmail providers scan email for malware before presenting it to you for your reading. A kind of we do it first then hand it off to you. I do have to caution you though, if you are going to post the header here. First put in on a notepad or wordpad first and replace addresses that could identify you and your network. [removed] should be [removed] in your post. and [removed] should be 212.xxx.xxx.xxx as well. Need to black it out because we dont want anyone trying to harvest your emails and addresses. Unfortunately this is still the world and the internet. Perhaps another has more information about headers and 127.0.0.1 and resources for you to chase this down. Good luck Kaz