Using classic Outlook for Windows in business environments
Dear LK_324
Thanks for using Microsoft products and posting in the Community.
About the number you want to know about Microsoft SMS Certification.
Microsoft cell phone authentication send SMS number is not a fixed single, there are the following common cases:
General SMS authentication code sending number: It may show up as a specific SMS number from Microsoft official, for example, some numbers featuring Microsoft brand or related business logos, like + country area code + carrier number and other similar number segments may be used to send cell phone authentication SMS.
Different numbers due to regional differences: Users in different regions may receive Microsoft Mobile Authentication SMS from different numbers. Internationally, authentication SMS may be sent using locally appropriate numbers depending on the country and region, for example, in the United States it may be a specific number that conforms to local numbering rules.
Today's cell phones may have a number tagging feature that you can use to see if it's a Microsoft authentication number. If it doesn't have this tagging feature, you can contact your cellular network operator to ask for the number to which it was sent.
Best wishes
Clark | Microsoft Community Support Specialist