WhatIsMyIPAddress.com Community

A long established contact in Germany is having emails to me returned with message 'host mx.bt.lon5.cpcloud.co.uk(65.20.0.49)said:522 email sent from 31.25.48.217 found on industry IP blacklists (Spamhaus/Invaluement/ReturnPath) on 2018/07.27 18.44.28 BST, please check for a listing on these external blacklists. Postmaster cannot help you if you are listed on these systems. (in reply to MAIL FROM command)'
I can receive emails from other sources and the sender can send to other recipients. Is this a problem with my IP address or the sender's and if it is mine I would very much appreciate some advice. I am a silver-surfer and not IT savvy!

Basically, your email provider is blocking their email provider.

Neither of you will be able to directly resolve the issue, however, both of you should contact your email providers to advise them that legitimate email is being blocked. In many cases just resend may result in a different IP be used, that hopefully, isn't being blocked.

They may need to start emailing you from a different email address.

They did try resend three times before resorting to snail mail to let me know of the problem. We'll try your suggestions.
Thanks.