Change Outgoing server settings in Mail on Mac
To change these preferences in the Mail app on your Mac, choose Mail > Preferences, click Accounts, click Server Settings, click the outgoing Account pop-up menu, then choose Edit SMTP Server List.
The servers available to you and the accounts that are using them.
Add , Remove
Add or remove a server. Don’t remove a server that’s in use by an account unless you’re ready to select or add another one immediately.
The description of the server appears in the Mail sidebar and any pop-up menu where you choose a server.
Your user name on the mail server.
Your password on the mail server.
The name of the mail server.
Automatically manage connection settings
Mail automatically manages settings for your email account in Mail, such as port numbers and authentication methods.
If you deselect this option, you can specify the following, as directed by your email account provider:
Some SMTP servers require computers that connect to them to provide a certificate proving their identity.
Allow insecure authentication
For accounts that don’t support secure authentication, let Mail use a non-encrypted version of your user name and password to connect to the mail server.