This article points to a Microsoft support article on how to use Microsoft's Scheduling Poll to schedule a meeting with people across boundaries such as companies, email environments, or time zones.
Scheduling Poll is a built-in tool in Outlook that allows meeting organizers to offer date and time options to attendees so that they can vote on their preferred meeting times. It provides attendees with multiple options for scheduling in a way that eliminates emailing back and forth, and is available in both the Outlook for Desktop and Outlook Web App (OWA).
NOTE: There are several different versions of both the Outlook Web App and the Outlook Desktop App. The functionality of the scheduling poll tool is not consistent across versions. If you would like to use Scheduling poll, but it does not function as laid out in this guide, please contact your IT personnel or 4Help for assistance.
Below is provided instructions from Microsoft on how to use the Scheduling Poll.
Find the best meeting time for everyone with Outlook Scheduling Poll - Microsoft Support