Just an update as some of the other similar threads are becoming very old now. Yahoo mails sent from my Pipex account are still not being received. Most of the other troublesome domains, as far as I can tell, seem better.
I'm sorry you're still having problems and that I can't get you any answers.
Please log in to My Account if you need to view or pay your bill, manage boosts and track your usage. From My Account you can also check your connection and test your line for any issues in the Service Centre.