What would be the criterion for sending a particular attachment?
You could do this manually from a browser to select an attachment and save to any drive including shared drives on your device.
If you want to programmatically grab an attachment you would need a condition and the attachment API. You could use Flow Designer to manage the trigger or condition on which to send the attachment and then use the GlideSysAttachment API to grab the file and send it. You could save to a mid server or other devices but some choices may be limited based on the triggering mechanism and if you do this as a server or client function.
Here is a mid server example https://community.servicenow.com/community?id=community_question&sys_id=0679b3b0dbfeeb00f21f5583ca96...
