This article assumes you already have a primary user account/email in Google Workspace and an Google Workspace alias email (alternate email) set up that you'd like to use as a "from" address in Apple Mail.

In this example, we'll use the user jaci@stringmarketing.com and the alias leah@stringmarketing.com.

1. ENABLE ALIAS IN GMAIL SETTINGS

In order to send email from your alias in the Gmail browser or app, first you need to enable it as an alias in your Gmail settings. 
  1. Log into the gmail account for the address that has the alias you want to send from - in this case, jaci@stringmarketing.com
  2. Go to Settings > Accounts
  3. Click "add another email address"
  4. Add the alias email address (in this case leah@stringmarketing.com)
  5. When you're done, it should list both addresses as options, like so: https://share.getcloudapp.com/rRubr1le
2. DESKTOP APPLE MAIL SETUP

SET UP MAIN  GOOGLE WORKSPACE EMAIL  ACCOUNT IN APPLE MAIL (DESKTOP)

If you haven't already set up Apple Mail for your main account, follow the steps below. If you have, skip to "SET UP ALIAS ACCOUNT IN APPLE MAIL (DESKTOP)" below.
  1. Open Apple Mail on your Desktop.
  2. Go to this Google support doc and follow the steps for Apple Mail on Desktop: https://support.google.com/a/answer/9003945?hl=en#apple-mail&zippy=%2Cset-up-gmail-with-mail-on-a-mac
  3. It will have you verify your account through logging in in Safari. When it's finished, it may take a minute for your email to populate into Apple Mail.
SET UP ALIAS ACCOUNT IN APPLE MAIL (DESKTOP)

When your main account is set up and working in Apple mail for desktop and/or iOS, you can add your alias email.
  1. In Apple Mail, go to Mail > Preferences :https://share.getcloudapp.com/RBuL8mnG
  2. Click on the "Accounts" tab
  3. Under "Account Information" find the email address pulldown and choose "Edit email addresses" https://share.getcloudapp.com/8Lu5X0gk
  4. Hit the plus sign and enter your Google Workspace alias email address and choose "ok" to save it. https://share.getcloudapp.com/6quY6zJy
  5. Check that it worked by composing a new message, hovering over the "From" email and choosing the email alias as the from address. https://share.getcloudapp.com/Jrux0oEl
  6. You should now be able to send from your alias!
2. IOS APPLE MAIL SETUP (IPAD OR IPHONE)

IOS will not allow you to use a Google Workspace email alias if you set it up using a "Google" account type. If sending email from your Google Workspace email address on your phone or tablet is a must, then you'll need to delete the account and set it up again using different settings.

In order to comply with Google Workpace security in setting up an IMAP account, you'll need to use an app-specific password.

SET UP APP-SPECIFIC PASSWORD FOR YOUR IOS DEVICE IN GOOGLE WORKSPACE

App-specific passwords can only be set up if you have 2-step verification enabled on your Google account. 
  1. To set up 2-step verification, follow the instructions here: https://support.google.com/accounts/answer/185839
  2. To set up an app-specific password for your iOS device, follow the instructions here: https://support.google.com/accounts/answer/185833?hl=en

SET UP YOUR GOOGLE WORKSPACE EMAIL ACCOUNT ON YOUR IOS DEVICE

  1. Next, you will set up your main email account on your iOS device. BUT, you will not choose "Google account" during the setup. In order to have access to email aliases, you need to set it up as an IMAP account under "Other Account."
  2. To set up your main Google Workspace email account, follow the steps in this tutorial.
    1. First, you will enable IMAP in your Gmail account settings.
    2. Then you will follow the instructions for iOS to set up your main Google Workspace email account as an IMAP account in the mail app on your phone or iPad.
SET UP YOUR GOOGLE WORKSPACE EMAIL ALIAS ON YOUR IOS DEVICE

Now that you have your main Google Workspace email account set up on your iOS device as an IMAP account, you can add your Google Workspace alias email address.
  1. Follow the instructions on this tutorial.
  2. Continue to the bottom of the tutorial for instructions on how to use the email alias to send email. 
  3. Celebrate! You're done!