Simple Mail does not support random selecting multiple email-addresses(usually via Ctrl- click) in "To", "Cc" or "Bcc" fields while compositing a message. But via defining "Group" in address book, users may add to those fields with fixed set ("group") of multiple recipients/email-addresses. You can create several groups to fit your needs.
How to:
- Click on "Preferences" icon on tool bar to open and select "Address Book" tab for setting.
- Click on "Add" to bring up the dialog, which can be resized to your likes.
- Give it a name in "Name" field and check the "Group" option for defining a new group.
- Keep on double-clicking contacts in address book for adding members to the group until it's done.
- Click on "OK" and there you are.