Email with Attachments

We have an application and part of this application has an email functionality.  In the app the user will navigate to a screen and on this screen will show a list  of access people and documents that can be created for the access persons.  The user will select what documents for each access person to create.  These are created dynamically with sql reporting and then converted to pdf's and included with the email,  Each pdf created is specific to the access person selected.  Because there can be a large number of emails selected at a time I am using the SendAsync for the emails.  This seems to work and they are created and sent in a reasonable amount of time. 
The problem is they now want to be able to add other file attachments to the emails, such as generic pdfs, word doc, excel, etc.  This works except for one issue.  When the user selects the what files to include as attachments I load the files to a temporary fold ...