p33-smtp.mail.me.com
The sender address -----@icloud.com was rejected by the server p33-smtp.mail.me.com.
The server response was: Authentication required prior to MAIL/SAML/SEND/SOML
Select a different outgoing mail server from the list below or click Try Later to leave the message in your Outbox until it can be sent.
Sending from: --------> ------@icloud.com>
macOS High Sierra (10.13.2), App Store