Instead of typing out each co-worker's email address individually, you can use the Office Online People application to create a?

You can create a Contact group.

Explanation:

This will speed up the process of sending emails to multiple people, as you won't need to select each one of them every time.

To create a contact group, go to your Contacts, click on 'New', and then select 'contact group'.

You'll be able to add contacts to this contact group, so the next time you need to send an email to a group of people, you can do so using the group.

You can also create multiple groups, for the different purposes of your emails.