“Our automated systems analyze your content (including emails) to provide you personally relevant product features, such as customized search results, tailored advertising, and spam and malware detection. This analysis occurs as the content is sent, received, and when it is stored.”
As said, they read and analyze your mail, mainly to sell it to advertizing companies. Google make money with this.
Sending plain-text passwords is rather interesting, tho. Could've at least optionally encrypted 'em with a key derived from smth known by the user only.
So obviously not to everyone's taste but if you have access to iCloud+ email, your mail isn’t scanned for sale (as per their US privacy agreement anyway), you get randomized email addresses available to give to places that you think might be spammy and you can link a domain to your account, although you’re only allowed 3 email boxes per user in your family per domain. Works well for me so far. Mind you because of photo storage size and devices backups I’m up to $3/ month from the original $1/month when I started.
Plus with Advanced Data Protection a lot of iCloud info is E2E encrypted. (Not email tho.)