Open Mail for me
The first time you open Mail, you may be asked to add an account. Select an account type or Other Mail Account, then enter your account information.
If you already added an email account, you can still add more. In Mail, choose Mail > Add Account, select an account type, then enter your account information. Make sure the Mail tick box is selected for the account.
If you’re using an account on your Mac with other apps, such as Contacts or Messages, you can also use that account with Mail. In Mail, choose Mail > Accounts to open Internet Accounts preferences, select the account on the left, then select the Mail tick box on the right.
You can Mail Support website