Thousands of people have your email address and you may have thousands of email addresses, but:

• Did you ever give your email address to those people?
• Did you give someone else permission to share it?
• Have you got permission to share other peoples email addresses?

Probably not.

When email addresses are put in the To: field of an email, they are immediately visible to everyone on that circulation list and sometimes automatically stored in your email address book.

You could be in breach of the data protection act if you do this, but there is a simple solution, use the Bcc: field, like this:

The recipients then only see their own address or ‘undisclosed recipients’

An Alternative

If you are a regular sender of bulk emails, you might want to consider email services like the one used by SUSTAiN. We use and recommend MailChimp, it is secure, easy to use and has a free version that’s suitable for most users. We are not sponsored by MailChimp, we just really like it.

Source: read this Guardian article on email and data protection