One area that separates a good executive assistant from an amazing executive assistant is the ability to get an Inbox under control.
At every turn of the corner in my career, the ability to master Outlook has proven to be an indispensible resource.
Here are some methods I’ve learned over time on how best to master Outlook:
Use message rules. One of the most efficient ways to use Outlook is to set up message rules that filter email into specific folders.
For example, you can set up a folder for a specific ongoing project and create a rule for messages containing the project name. They sort themselves directly into that folder. These rules save you from having to read e-mails multiple times, and they help keep relevant information at your fingertips in a central location.
Don’t use work email for personal messages. Personal messages eat up a large portion of your day, if you let them. If you do receive personal messages during work hours on your e-mail account, make sure to filter them into their own folder so you can deal with them as time allows – and that doesn't mean on the employer's time.
Integrate Outlook calendaring and messaging. From within your Outlook email, you can click on an e-mail and turn it into a task or an appointment on your Outlook calendar. That saves several steps in time management, and it turns e-mails into actionable items immediately.
Teach your boss to use flagging and priorities in her Outlook e-mail. Flagging with priority levels helps you know how important your boss considers an email or tasks he sends you. It also helps your employer learn to think over what truly is important and to prioritize more effectively.
This site is a great discovery. A website where every woman that has a handy stash of top tips she's worked out for herself to make life easier -- let's face it, we all have our little secrets -- can share them with "the girls". 
