GrowlMail is a plug-in for Apple Mail that posts a Growl notification every time new mail arrives containing the text of the message.

Features:

• A toggle controlling whether GrowlMail is enabled.
• A toggle controlling whether GrowlMail will only notify about new mail when Mail is in the background. If off, GrowlMail will notify even if you are working in Mail at the time.
• A toggle controlling whether GrowlMail will only notify about new mail in your Inboxes. If off, GrowlMail will notify about messages in any mailbox. Having this option off can be annoying for some IMAP accounts (as messages may appear in multiple mailboxes, and so cause multiple notifications) and for messages not recognized as junk by Mail.
• A choice controlling whether GrowlMail posts one notification per message, or a single notification for a whole batch of messages. If set to “Let GrowlMail decide”, GrowlMail will send one notification per message unless a bunch of messages come in at once.
• A format describing the title of each notification.
• A format describing the description of each notification.
• A list of accounts with checkboxes. GrowlMail only notifies about messages received on accounts you have checked.

Requirements:
OS X 10.9+
64-bit Intel

Also available is:
Version 1.3.8 for OS X 10.8.5