Use Hide My Email in Mail on Mac
If you subscribe to iCloud+, Hide My Email allows you to send and receive messages without having to share your real email address by using unique, random email addresses that forward to the email address associated with your Apple ID.
Tip: You can see and manage your unique, random addresses, or create new ones, in iCloud Preferences on your Mac or in Account Settings on iCloud.com.
Send an email using a unique, random address
When you write a new email message, Hide My Email allows you to create a unique, random address directly in the Mail app.
In the Mail app
on your Mac, click the New Message button 
to compose a new message.Add a recipient and subject for your message.
Messages you send from a unique, random address can only be delivered to a single recipient.
Move the pointer over the From field.
Click the pop-up menu that appears, then choose Hide My Email.
If you’ve never sent this recipient an email from a unique, random address: A new address appears in the From field.
If you previously sent this recipient an email from a unique, random address: The address used previously with this recipient appears in the From field.
Write your message, then when you’re ready, click the Send button
.
Receive an email sent to a unique, random address
When you receive an email message sent to a unique, random address, you can do any of the following:
Reply to the message: The unique, random address where you received the message is used by default when you reply.
View and update your Hide My Email settings: Click Settings in the banner shown across the top of the message, or Control-click Hide My Email in the To field, then choose Go to Hide My Email Settings.