The recipient email sometimes changes to alias name and sometimes

[OfficeUser]

When I try to order my sent emails by grouping them by recipient, the same
contact appears twice, once under the email address and other under the Full
Name. How can they be grouped together?

 

[Russ Valentine [MVP-Outlook]]

Your post is too unclear.
Sent Items displays messages, not Contacts.
You posted neither your view nor your Outlook version.