Hi @Tammy Wong ,
According to your description, this issue only happens to some specific users, do these users have any similarities (such as all your contacts or others)?
I did lots of tests on my Outlook 2016 for your issue, and according to my tests, when I add a member to my contact manually, the auto-complete list could show the "name (name@keyman .com)" and it also could display in the recipient field like below. Except this way, I haven't found other way to achieve the same effect.
Besides, if the recipient is just a member in your organization and not your contact, it would show the name <name@keyman .com> in autocomplete list and only show name in recipient field, which matches your description.
If this is not your case, please give me more information about your issue and I would give you more targeted help.
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