Miscellaneous topics that do not fit into specific categories.
If this is a consumer license of Office 2016, you can try the e-mail address you used at the time. The mail account doesn't have to be able to actually send mails, as long as you can sign in to https://account.microsoft.com/services .
If you run into activation issues, see https://support.microsoft.com/en-us/windows/activation/activate-microsoft-perpetual-products-using-the-product-activation-portal .