New reason for 550 error?

[#1]

Recently I have seen many 550 errors when trying to send email. The common factor in all of them is that the addresses are of the form "Joe Bloggs" <joe@bloggs.co.uk> and the messages go without problem when the address field is changed to joe@bloggs.co.uk .  I have often sent messages with similar addresses before, and without problems, so this seems to be something new.
I'm using a version of  Eudora which hasn't been changed or updated for a long time, so if there is a change somewhere, perhaps this is at plusnet.

[#2]

There's not much to go on from the information you've provided. Ideally I could do with knowing:

• The email address you're sending from.
  
• The email address(es) you're sending to.
  
• The Internet provider you're connected to.
  
• The outgoing/smtp server that you're sending the email via.
  
• The full error message or failed delivery notice that is returned.
  

That lot should probably give me a good idea as to where the problem lies but due to the sensitive nature of some of the answers, you might want to consider raising it as a support ticket on your account

[#3]

Thanks. Will raise a ticket.