I have the user's email address but don't know what property I should use when setting the value of a Person.Grouop field.
I do not know if I understood you correctly. To be able to query (get data for a particular user profile attributes) a user profile using the Office 365 query user profile action you HAVE TO provide user e-mail address for the field: "User name (Email address)" (this is the only way to configure the action).
But if you are asking what value you should insert to the "People or Group" SharePoint field to set its value, then this is easier - you can either use e-mail address or account name.
Thank you Tomasz, "AccountName" property is what I was looking for. However I also did not realise I can simply use the email address in the Property or Group field instead so that makes my life even easier!! Thanks
Retrieving data ...