What is an alias?
An alias is another email you can send and receive emails from.
Copper requires you to log in with your default email address. To figure out what is your default address, go to your Gmail -> Settings -> Accounts and it will show up in that view.
Below you can see Harrymoonshine1@gmail.com is the default and firstname.lastname@example.org is the alias.
This means you must sign up with Copper using the default email: Harrymoonshine1@gmail.com, you will still be able to see emails from the non-default email: email@example.com in Copper.
Copper scrapes/pulls in/sync emails in from your default email and all the aliases you have. If you do not want to pull in emails from all aliases into your Copper account, you will have to delete them from your Gmail.
Confused? Imagine your "default" email address as a bucket and all the aliases as pennies in that bucket. Copper scrapes everything in the bucket.
How to add an alias:
1. In Gmail, go to settings
2. Go to Accounts and Import
3. Click Add another email address
4. Type the email you want to sync
5. Go to your Inbox for the email you entered and open the email that was sent to you, follow the instructions in the email, and you are done!
More instructions on adding aliases from Google