Sending emails with Gmail

Visit https://mail.google.com/mail/u/0/#settings/accounts to access your Gmail "Send mail as" settings

Once there, click "Add another email address" and a popup like the one below will show up:

Name: Enter a name you'd like people to see when they receive an email. If this is a "support@project.com" email, you might want to name it "Project Support"
Email address: The email inbox you added in Sidemail, for example "support@project.com"

Then click "Next Step" and you'll see: 

Within Sidemail (after you create your inbox), we'll show you the username and password required for sending emails.

Thats all!

On the account page https://mail.google.com/mail/u/0/#settings/accounts, we recommend using the following setting: