The myMail app through 14.30 for iOS sends cleartext credentials in a situation where STARTTLS is expected by a server.
https://news.ycombinator.com/item?id=35845308
https://mailbox.org/en/post/mailbox-org-discovers-unencrypted-password-transmission-in-mymail
https://apps.apple.com/fm/app/mymail-email-app-for-gmail/id722120997