Hi @Vikram Doss ,
What's the outlook client you are working with? In order to further analyze your issue and perform more targeted tests on my environment, please provide me with more detailed information about your issue(detailed client information, account type and others).
I understand that you would like to remove an email address in Suggested Searches when you type it in the search field, is it right? If so, as I know, this list would display the items that you type recently or the address that you usually use(contact or search), if the item is a history like below, based on my research, for Microsoft 365 account, we could delete this item in owa(Settings>View all outlook settings>General>Privacy and data>delete history) , then the history items would be deleted in owa and outlook client.
Considering you have tested on your owa, could the email id still in your owa after that? If so, I think the email address is actually not your history that mentioned above, and it may be stored in your mailbox. Based on my experience, the list could also display these addresses that you usually use, I have also tried to research a lot and perform many tests to delete them, but it would still be displayed there even I deleted all messages with this address. Also for the option of register as you mentioned, it could only delete the recent search list instead of this item. So I'm afraid there may be no option that could delete it in Outlook. In this case, we could try to post an idea in our uservoice, which is the official platform that Microsoft collect the suggestions on Outlook, it may increase the priority for our engineers to create a possible option or feature that can be included in the future updates of the program. Thanks for your understanding.
Hope that would be helpful to you.
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