Subject 'This one received also', Account: ***********, Server: 'relay.plus.net', Protocol: SMTP, Server Response: '552 QzFZ1p0052TW3YY01zFbgA message rejected due to spam or virus. If you believe this is in error please login to your portal or contact your ISP support team.', Port: 25, Secure(SSL): No, Server Error: 552, Error Number: 0x800CCC6D.
I received this error message when replying to an incoming mail. Creating a new mail message with the same recipient sends OK.
The incoming mail has "SPAM" inserted in the subject field. No idea where this is being added.