We are trying to set up office 365 to send email from our azure account.
Are our Outbound IPs shared with other azure users or not?
https://learn.microsoft.com/en-us/azure/app-service/overview-inbound-outbound-ips
To find out if the outbound IPs that are shown in the properties area of my portal are shared with other users or do I have to buy a dedicated static IP address to make sure no one else is using them.
It seems that you refer to the outbound IP of web service in Azure. Azure App Service is a multi-tenant service, except for App Service Environments. Apps that are not in an App Service environment (not in the Isolated tier) share network infrastructure with other apps. So the IP address lists used for the web app are possible to share with others.
Unless you use an Application Service Environment (ASE) you cannot guarantee that the inbound or outbound IPs will change, However, you could control when the IP address will change. The set of outbound IP addresses for your app changes when you scale your app between the lower tiers (Basic, Standard, and Premium) and the Premium V2 tier. For more references, you could see steve's answer here.
