My web sites are hosted on a shared hosting server and it sometimes gets blacklisted by various monitoring systems. The different monitoring companies result in different organisations rejecting emails sent by the server. The host has tried giving a different IP address to outgoing email and that works for a while but redirects set up on the server use the server IP address this has led to rejects for email from baildonmoor.org.
Hopefully that is now a thing of the past. I now have my own IP address for the accounts within my control. With a bit of luck that means that it will not get blacklisted unless sites within my control start doing silly things.