The .aqproj file is the native file format for exported projects in this version. The file can be sent directly to other AQ users outside your company. Be aware these files contain all elements contained within the original project. Double clicking directly on the aqproj file or, clicking the embedded link to the file within an email, will open the project within the AQ application.
If the file does not import successfully the recipient may need to reset their AQ file associations on the system. Instructions for setting your default file associations can be found here. How Do I Import a Project?