Actually in a previous version I would use href’s to open a file, after the user selects a file to open. The file is prepared to be in the users temp directory. This works, I only need to put in a normal href, pointing to the file. Issue is that in that case all the files (attachments in a email) need to be prepared before the email can be shown. This works for a small number of attachments, not for a large number of attachments. In that case after selecting the email, the user is presented with a long delay, during which the application is not responding. So I was looking for a way to prepare the attachment after selection, so the delays for the user would be more acceptable. You are right that it is not a safe way to do with a function call inside a href. Maybe I should go back to the previous solution and use Thread() to solve the non-responsiveness of the application. Problem is I don’t know how much I can trust the Thread() option. Any tips?