On Tue, 19 Oct 2021 at 10:49, Bill Hill mail@wbh.org wrote:
Have you got a reverse DNS record for the MX ip address?
The MX IP's will be those of (in this case) 123-Reg who handle the mail forwarding, and they do have reverse DNS, eg: https://mxtoolbox.com/SuperTool.aspx?action=ptr%3a94.136.40.235&run=tool...
But they don't reference the domains in question, is that an issue?