This is why you should not use Google free services for anything important. Google could turn them off tomorrow. You have no contractual guarantee against that.

Do mail through IMAP. All your devices can sync to a IMAP server. The IMAP server built into Android isn't bad at all. Use Thunderbird on desktops and laptops. Most ISPs offer free IMAP. Or you can get your own domain and use IMAP from a server on it. No ads, too.