Messages Received with Bare Linefeeds is the number of messages received that contain illegal bare linefeeds in the SMTP ...

Messages Received with Bare Linefeeds is the number of messages received that contain illegal bare linefeeds in the SMTP DATA stream. Linefeeds not followed by carriage returns aren't allowed in SMTP communications. In some cases, Exchange can apply lossless encoding to such messages to prevent the bare linefeeds from being transmitted to other servers.