Google Workspace mailboxes connect with Sign in with Google, so you never share a password.
Once, for your whole Workspace
Your Workspace admin marks mailzy as a trusted app. The steps are on screen in Mailboxes → Sending accounts, with a direct link to the right page in the Google Admin console.
Then, for each mailbox
- Open Mailboxes → Sending accounts and choose Google Workspace.
- Press Sign in with Google and sign in as that mailbox.
Repeat for each mailbox you want to send from.