I have a love-hate relationship with email on the Mac. I cannot tell you how many different mail apps I've tried - Mail.app, Thunderbird, Postbox, Sparrow, Airmail - the list goes on. Each of those applications has their own unique way of dealing with the never-ending onslaught that is my inbox, however, each time, I come back to Mail.app. Why?
Mail.app is actually a pretty decent application for dealing with email. However, there are some areas where it's seriously lacking when compared to it's peers.
Each one of aforementioned mail applications has its own intricacies for making email presentable and notifying you of new messages and until Notifications on OS X Mountain Lion, Mail.app was seriously lacking in visual alerts. Even after Notifications was introduced, the toast that pops up in the upper right quickly grew into an annoying reminder of just how much extra work I had ahead of me. Put simply, a constant reminder that Inbox Zero was quickly slipping away was not helpful - at all. Think of the kid who keeps saying, "mommy, mommy, mommy, mommy" a hundred times per day. Sure it's cute at first, but after a while it just grates on your nerves. I needed something that would not just notify me of new messages, but would actually let me take action on them without having to open the Mail.app window.
Low and behold, I found Herald. It's just what I needed to give my Inbox Zero habit an extra little boost. When I receive a new mail notification, I get an action bar at the bottom of the notification window which allows me to reply, reply to all, forward, mark as read, archive, flag as spam and delete the email. There's even an action item to open the email in Mail.app if you choose to, although you can read an entire email directly in the notification bar - something else that's an incredibly cool timesaver.
There are different styles for the notification window. You can choose the amount of opacity, the background shade, text color, display font size, how much information displays in the header of the notification toast, and which of the aforementioned action items show at the bottom of the notification toast. There are just enough options to give it personality without it being so granular you're constantly tweaking it (another huge timesuck).
For a free plugin that's well coded and doesn't cause random crashing of Mail.app, this sure is a great addition for those of you who, like me, try to squeeze every ounce of productivity out of their inbox. Inbox Zero fans rejoice!
The next plugin is more of a convenience than anything else. With Herald, I don't often have my Mail.app window open, but when I do, I like the design of my inbox to show me, at-a-glance, exactly who the email is from without having to focus my eyes on the sender's name.
What I loved about Sparrow was that I could see an image of the sender next to the email sitting in my inbox with a fleeting glance. Face-to-Face is the perfect plugin to give me that kind of detail quickly for Mail.app. By default, Mail will check the images in your address book for an image associated with a particular sender and Face-to-Face does that too. What makes this plugin unique is that it will also pull images from Gravatar, Facebook, your company's website and Face-to-Face's own database. Receiving an email from a company rather than an individual is no longer anonymous.
You'll choose how you want to set up the plugin when you first install it, however, if you want to change any options post-installation, you can do that with a handy View menu item. From there you can change any of the original installation preferences.
Face-to-Face really makes my email a more personal and intimate experience, especially since I get a lot of email from individuals (as opposed to companies). I can't imagine using Mail without it.
Both Herald and Face-to-Face are free plugins and have very intuitive installation processes. You don't have to mess with your
~/Library/Mail/Bundle directory except when you want to uninstall either of these plugins, although Herald does offer an handy uninstaller .app in the download directory it creates.
I highly recommend both of these plugins if you want to breathe new life into Apple Mail.
Source: Apple Mail Plugins and Tools