MailTags 是个 Mail 2.0 的插件，现在其 2.2 最新公开测试版本为 beta 3，可以让用户在邮件上新增 metadata、标注、优先顺序标志、到期日期等等。安装之后，在每封邮件右上角会有个 MailTags 内嵌的快捷图标，点击便会显示侧边栏，在这个方便而定侧栏中可以对此邮件做些额外处理。 新版主要新特性除了兼容新版 Leopard 之外，还包括：

iCal Support
- Create To Dos and Events in iCal directly from Mail and maintain the link between the original message and the items in iCal.

IMAP support
- Save your tags to your IMAP servers so you can access them from multiple computers.

List Display
- Display your tags in extra columns in the message list view. See due dates as they approach.

Works with Mail's Rules
- Set tags automatically as you receive Mail by using MailTags actions when creating a Mail rule. Use with Mail Act-On to create keystroke rules to tag messages.

Works with Mail's Search
- Search for your tags by using Mail抯 search field, narrow the search to on keywords, projects or notes. Use simple and/or logic to find tags.

Works with Mail's Smart Mailboxes
- Build smart mailboxes that search your messages for keywords, projects and due dates.

Applescript Compatible
- Construct Applescript work flows that access your MailTags data to use them in other applications.

目前 2.0、2.1 版本用户可以免费升级到这个最新测试版。

下载：indev.ca/MT_Leopard_2.2_PublicBeta3.dmg