Notify contacts of email address change

Question

How do I notify my contact list of my email address change. Do I have to select every contact individually?
How many addressees can be included in one email?

Answer 1

To answer your second question first, Apple Mail doesn't impose a limit, but your mail provider (eg, Gmail or whoever) might.
There are a couple of ways to notify contacts of changes. Address Book has a built-in method. First, make sure your contact information in your card is correct (delete any old information). 
Next, if you need to send your email in multiple batches (because of a mail provider limit), group your contacts into separate groups of under that limit (eg, under 50, or 100). Make a number of groups called, for example, "All Contacts 1", "All Contacts 2", then multiple-select a set of contacts and drag it into the appropriate group.
You can now use the File - Send Updates menu to choose the groups you want to send to, and customise the message. Your contact details will be enclosed in a VCard file, which people can add to their contact programs.
To send the email manually, just start a new email and in the "To" field, type the name of your first group. Compose and send the message. You can either copy and paste the message text if you need to send to a second group, or use the Resend button on your sent mail to change the destination.
One more thing - For this kind of mass email, I generally favour putting my recipients (contacts or groups) in the BCC field, and setting the "To" to my own address. That way, people don't see each other's email addresses (which can be a privacy issue for many people).
best,
Matt