Outlook does not use the right email address

I had this question after viewing Autocomplete email addresses changing/sending to strange address in Outlook 2010.

I am using outlook 365 on windows 7. I have  a strange situation with one email adress i use very often. When i type "Kurt" in the Adress field, the autocomplete shows me the correct email adress "kurt.xxxx@correctdomain.com". When i hit enter, outlook puts a very old adress of this person "xxxxx.kurt@olddomain.com" . In my address books i have no longer an entry with "xxxxx.kurt@olddomain.com". I do not want to clear the whole autocomplete list. Any proposal  to elimante xxxxx.kurt@olddomain.com ?

Thanks

Gilbert