Is self-sending email spam legal?
When email spammers put something in the "From:" field
but not their own email address (for  fear of being shut down)...

Self Sending Spam

When a spammer sends a message, he has several goals. First, the message must make it through one or more spam filters. These filters may scan the message for "spammy keywords" at an ISP, a web host and at the user's own system (and potentially other places as well).

An especially annoying type of spam is called a "self sending spam". This is a spam message which you receive and the "From:" address is your own email address, or some variation of it. For example, davesmith@example.com might receive an email with a FROM: davesmith@anotherexample.com

Sometimes the email has your exact same email address in the "FROM:" field, making it appear you've sent the message to yourself.

Why do the spammers bother to do this?

It makes the receiver more likely to open the message -Studies have shown that people like seeing their own name. Researchers have found much higher response rates from emails sent in which the sender had the same first name as the receiver.

It appears to make it harder to trace the spammer -Actually, spammers tend to forge just about everything in the email message, and thus are often difficult to trace. However, making the "From:" address the same makes it appear hopeless to try and find the sender. After all, it is obviously (unless you look deeper into the message header) wrong. So why do any more searching?

It confuses some automated spam reporting programs and scripts - Some programs and scripts have the ability to report spam (automatically or upon command) to various places. The software attempts to determine who sent the spam so it can be reported to the ISP, web host and anyone else who can do something about it. Some of the less intelligent spam reporting software will become confused by self-sending spam and actually cause the receiver of the spam to report himself as a spammer (this actually happened to me once).

It looks more legitimate - Spammers have to put something in the "From:" field - it may as well be your name or something close to it. They cannot use their own email address (for fear of being shut down) and some strange, random string of characters is not very appealing. So why not just use your own name? It sure makes creating the spam message easy.