Let’s say that you have consolidated multiple email addresses into your Gmail account. Great. Now you have all your email in one place. But sometimes you want to be able to send email using an alternate email address. The Gmail web client makes that easy. You just go to Settings > Accounts > Send mail as > Add another email address. Once you go through the verification process, the email account will appear in the list. You can specify which account to “make default”. You can also tell Gmail what to do “When replying to a message”.
But what about Apple Mail? In the latest version of Mail 14.0, you can add an additional Email address under the Google Account Information tab. Go to Mail > Preferences > Accounts > (your google account) > Account Information > Email Address > Edit Email Addresses… You can add any email address you want, however, only addresses that you have already added to your Gmail account will work. You can also specify the name that appears next to your email address.
When your recipient receives your email, the from name and email address will appear.
Remember, this is not hiding your identity. Anyone who receives your email can just look at the email headers to see the authentication user who sent the email. For that matter, the headers give away your physical location in the form of your IP address. It does afford you a little bit of self branding and it allows you to have your email address and your username be different.