Hello, Thanks for previous assistance on this topic but the structural issue remains. I am able to add certain email addresses to my Address Book and then modify those entries so they appear in my addressing hierarchy with tags and names as I need them to be. But in the attached examples, you will see that some email addresses from the same domain add, and others do not allow me to add. This has the unfortunate side effect of having an Address Book that is 70% usable and 30% in complete chaos because the manner in which many incoming email addresses are structured is often of no use in trying to keep order. I attach multiple examples of the problem. The prior suggestions of turning off email address and showing User entry name only does not really solve the problem when I am unable to modify an address that is not actually saved in the Address Book. I have also tried multiple times deleting Thunderbird and the related entries for IMAP mailboxes and abook.mab address books. I even rebuilt the entire mailbox to see if that would help. Nothing worked. This was a problem some time ago, and then it disappeared and now it has reappeared again. Assistance from the expert users of Thunderbird would be appreciated. My version of Thunderbird is 142.0 and I am using the Windows 11 Operating System. Yours sincerely, Mansoor IJAZ