Blind Carbon Copy

One of my biggest geek pet peeves is when someone sends an email to like 30 people and put all the addresses in the To: field. Whether the email is informative or junk does not matter. The issue is that there is often no reason to have everyone's email address exposed for everyone else to see. This raises a few issues:

• What if I didn't want everyone else to know my email address, and I only gave it to you because you're my friend? Now everyone else on the To: list needs to know my address.
• Now any recipient of that email can just click "Reply to All" and send even more often useless email to fill your inbox.
• If one of the 29 other people on the email decides to forward the email, now even more people can see my email address. Have you ever seen when you get a forward, that you have to scroll through all the other people that the email came from? This is often how email addresses are harvested for spammers.
  

Read more about Email Netiquette 101 (See especially Rule 12 -- "Don't expose your email routing list to spammers"), Bcc etiquette, and read some other content here.