I have been piping (redirecting) emails from my "???@lygra.xyz" address for several years it has suddenly stopped and is being rejected by bigpond.com. The service spamhaus doesn't list it as blacklisted. See below.
From: Mail Delivery System <Mailer-Daemon@eigbox.net> Sent: Saturday, 11 January 2020 11:03 AM To: email@example.com Subject: Mail delivery failed: returning message to sender
This message was created automatically by mail delivery software.
A message that you sent could not be delivered to one or more of its recipients. This is a permanent error. The following address(es) failed:
firstname.lastname@example.org host extmail.bigpond.com [188.8.131.52] SMTP error from remote mail server after pipelined MAIL FROM:<SRS0=jIOGUX=3Aemail@example.com> SIZE=6356: 550 5.7.1 lygra.xyz Sender domain rejected. IB500