This is a question related to my previous question of how to create an item using emails. I have set that up and any emails sent to the email address creates an item using that email as an attachment. Now I was looking to update the email attachments when updated emails are sent as we don't want to create a new item for it. Is there a way to check if the same ID number is passed in the subject line then that particular item's attachment is updated? Can this be done through workflow? Any suggestions on how to implement this?
This is not default functionality. Personally, I would not use mail enabled lists anymore but create a timerjob / console app that reads an email account, does the required validation and business logic and stores the items in the list.
However if you want to keep using 'mail-enabled' lists. Try working with an event receiver. Everytime a new item is created in the list a custom piece of code runs. In this code you can check for the ID's and optionally move the attachments.
Creating a custom workflow (visual studio workflow) is possible as well but this will much more complicated than creating an 'event receiver'.
Also take a look at SPEmaileventreceiver. https://msdn.microsoft.com/EN-US/library/office/microsoft.sharepoint.spemaileventreceiver.aspx