If you need to add someone to a discussion in an email there’s now an option to ‘@’ mention them.
That’s quite useful for when you need to introduce someone to another contact or list a few of people’s email addresses in a message quickly.
If you mention someone with a + sign instead of the @ symbol, that contact will automatically be added as a recipient of your current message.
You can turn it on by choosing the option in the menu that pops up when you click the gear icon in the top right of your inbox.
When you @mention the contact within your email, the recipient will be able to click on the contact and it will open up in a new compose window so they have the option to email the contact themselves.