Outlook For CiviCRM - How to bypass activity confirmation dialog?
Outlook-CiviCRM documentation says that the confirm dialog box can be turned off through UI.
Prompt for All emails?: If this setting is enabled - While sending emails, you would always be asked whether you want to record this email in CiviCRM (A small pop up confirmation box would appear). If you don't want to be asked every time and just want to record every email you send, turn this setting off

HTH
Pradeep