Many other IMAP clients can be configured to store your sent items in a specific IMAP folder. For compatibility with these systems, you may have to tell netMail which folder to use for storage of messages sent through it.
To change the default setting, which stores the sent messages in a "Sent Items" folder, simply select another folder from the menu and click the "Save Changes" button at the bottom of the page.
Some other IMAP clients refuse to honor the visibility flag of folders, and thus you may be used to seeing folders in your IMAP client that the IMAP server has made invisible. To get the folders you use to show up in netMail and most other IMAP clients, you must mark them as visible here.
When a message has an attachment that is really some kind of media file, netMail can automatically embed it into the message view. This can have an adverse effect on your browsing performance, so unless you are on a broadband connection, you probably won't want to embed anything besides attached images. If you are on an extremely slow link (e.g. a mobile phone) then you may want to disable media embedding completely.