Encryption hides the contents of an email, but not the metadata about the email used in the communications process.

SMTP encryption hides the content of the email as it is being transferred between computers.

End-to-end encryption is where the email is encrypted by Alice’s computer and only decrypted by Bob’s computer.

While SMTP encryption alone is helpful in the context of a monitored link, both the sending and receiving computer have the email in raw form. Therefore any computer in the chain can examine or copy the contents of the data. If the email is hosted on a typical email service provider, free or paid, the contents and metadata is not hidden from the provider.