How do I add an attachment to my message?

Why add an attachment to your message if this creates a heavier message for the recipients to download? Furthermore, adding an attachment makes it difficult to measure if the recipient has opened or is interested in your message. 

There is a better way, namely, linking to a document in the module Documents. The uploaded document will be opened in the recipients browser and you will be able to measure who clicked on the link and who is therefore interested.

Linking a document in the editor of messages