You can use Hiri to connect to Exchange, Office365, or a Microsoft email account (Outlook.com, Live, Hotmail). Other email providers, such as Gmail, Yahoo, etc are currently not supported.
Download the setup executable from the link above and run it. Simply follow the wizard to install the application.
You'll first need to enable launching apps downloaded from the Web. Go to Privacy & Security → Allow applications downloaded from, select Anywhere.
Download the DMG package from this page. Open the package and drag Hiri into the Applications folder. Once it is installed, you can launch it from Spotlight.
Download the .tar.gz file from this page. Unpack the archive somewhere in your system. Open a terminal and launch
hiri.sh from the application folder.
To start Hiri more easily, you can also create a desktop entry from Hiri by going to: Settings → General → Create desktop entry. From then on, Hiri will appear in your launcher.
Hiri is free for personal use and for the first 5 users in a company. Have a look at the pricing page for more info on purchasing.
The full license text can be found here.