AG1562 wrote:

I have just begun to encounter a problem in as much that if I try to
send an email to an address not in my address book Outlook stops it
being sent unless I create a new contact.

What makes you think Outlook stops it? Exact error message text, please.

This has never happened
before and surely can not be right

It's not. Outlook doesn't care one whit whether or not the address you
place in the recipient field is a contact.
--
Brian Tillman