Be Polite Use BCC
Hawkwings has a post about controlling HTML in email. This is one of those things that tends to annoy me, people who send emails with lots of HTML formatting just to make them look nice. So, you get emails in your inbox that are huge (in size) but only contain a few words, and take extra time to retrieve. Really I just need the words, not flowery stationery. (Agreed this is a preference thing but. . . ) Hawkwings walks through the steps to make everything plain text and fix this problem.
This however reminded me of a larger pet-peeve of mine. BCC vs CC. Have you ever received an email (spam or otherwise) that contains extra names in the address field. Sometimes I get these from people I know, with like 60 addresses. The hey I just changed my address and I want to let everyone know here it is. Well this is a HUGE problem. Why? Because now 60 people all have your email address, some of which you probably do not know, and it only takes one of them to have a virus to have all 60 addresses sent to some spam service. (The most egregious error I have seen in this regard, was by the book store, which copy and pasted all of the email for all of the faculty into one large to field.) Spammers actually pay for email addresses, and the practice of CCing people rather than BCCing them helps them to collect all of these addresses.
There are two ways to address an email to more than one person. CC-which stands for carbon copy and BCC which stands for Blind Carbon Copy. The key here being “blind.” If you CC someone, everyone gets all of the email address, all 60 of the people. But if you BCC them people only get their own. Problem solved. I will admit there are uses for CC. For example committee work when you email a group and want people to respond to the whole group, so they need everyone’s email. But, as a general principle you should BCC people and only CC them if you have a specific reason.
UPDATE Read the comments below as Mark and David have important things to add.