HI louij2, thanks for the message and sorry to hear that you are having issues with this. Have you managed to get this resolved or still having issues with this, did you check this on spamhous - https://www.spamhaus.org/query/ip/ ^Chris
As you have confirmed the service is working on the webmail service. Can you clarify if this is happening on one device in particular or other devices? If it is happening only on the one device regardless of the app or email client used, then, is that device using a firewall or antivirus or any other service that monitors your device connections?
to fix my issue on my iPhone I had to delete account and then add my blue yonder account again.
the IMAP & SMTP settings are pointing at imap4.blueyonder.co.uk smtp.blueyonder.co.uk and this is the only mail server I can get it to work with. The instructions on your website don’t resolve my issue.