Every so often I get one of these emails in my inbox. Today's example:

Hello!

I have decided to join the ranks of half the people I know, and switch to Gmail.

Therefore, effective immediately, please start emailing me at *xxxxxxx@gmail.com*.

I'll keep receiving verizon.net emails for another month.

I hope you're all well and that you have a lovely day!

Nothing unusual? Except the person did a "send to everyone on my address box" mass mailing. I got it only because I am on an email list that this person also belongs to. So, now I have the name and address of everyone in his address book. A quick glance gets me these information:

political affiliation -- a presidential campaign list email
closer friends' name and emails -- people who appear multiple times with personal and work emails
social affilations -- other social email lists
interest or profession -- noticed several emails from people in a specific industry
possible a parent -- small number of emails from a school (if large number, he may work there)
personal style -- subscription to specific stores' emails

Not a mistake that one should be making ! Your homework -- look at your own address book and see how much "personal" information is in there if someone gets hold of just the list of names and emails.