Wrong name appended in brackets after email address of recipient - needs to be removed

Whenever I start to compose an email to a specific recipient, OS11 Mail appends an incorrect name in brackets after the recipient email address which has now become a source of frustration. Following Apple support suggestions I have removed the address from the contact list; I have ensured that it does not come from the Mail Preferences accounts, I have removed Siri making email address suggestions. After all this, when starting to type in the address the same incorrect name is appended. I have considered a complete rebuild to remove the issue, but we have a total of 8 Macs on the network and as I note that all Macs, iPads and iPhones are doing the same thing, I suspect I would need to rebuild them all and destroy all mail history (IMAP so fully shared) to stop this annoyance. Can anyone advise where this name is stored and how to stop this occurrence?