A personal Gmail account connects with an app password: a separate password Google makes for one app, which you can remove at any time.
- Turn on 2-step verification in your Google account's security settings.
- In the same place, create an app password.
- In mailzy, open Mailboxes → Sending accounts, choose Gmail, and enter your address and the app password.
Removing the app password in your Google account disconnects the mailbox from mailzy.