In the mobile app, you can create new contacts while writing a smart mail. This helps you send emails on the go, and here's how to do it:

In the app, go to the mail tab > click on the compose button on the top right corner > select Quick Compose.

Next, type any new emails in the To line, and click on Enter. You will see the pop-up. Choose Create Contact to add the email as a new contact now, or choose Later to send the smart mail without adding a new contact.