Spoofed E-mail addresses
Many viruses and spammers "spoof" the e-mail address in the "From:" field. It's trivial for a program to pick out an e-mail address and say the message is from that address.
This can cause various problems. The most common one is when the spoofed e-mail is bounced. In the early days of the Internet, it was considered good manners to tell people if they sent an e-mail to the incorrect recipient, so servers had automatic bounce messages. Most have turned off this feature due to spam,* but there are a few that still keep it operating. If a message is sent to these servers, you may get the bounce message.
A typical bounce message is shown below.
There are several things to remember about bounce messages.
Other ramifications of spoofed e-mail addresses:
You must be alert to this issue.
* In addition to filling inboxes of people with bounce messages, it also allowed spammers to gather e-mail address A spammer would sent messages to millions of random addresses (e.g., firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, etc.) at a server. They would get bounce messages for 999,900 of these. Then they'd compare the list the sent to the list of bounced messages and find 100 addresses that didn't bounce. Viola -- a hundred good addresses to sell to other spammers.