9. Choose "I want to select one of the keys below for signing and encrypting my email:" and select your key.
10. Choose Continue
11. Choose Done
12. Login to your webmail. Go to Settings / Preferences / Security & Keys, check which setting you are using for: "Server encryption method for unencrypted emails" See if you use only "PGP/Inline" or the combined "PGP/Inline & PGP/MIME (for attachments)" ?
Start ThunderBird. Go to the Enigmail-menu and click on Preferences. -Click on "Display Expert settings and menus" -Click on the Advanced tab
If you use PGP/MIME as encryption method, make sure "Only download attachments when opened" is unchecked, as seen on the picture below. If you use PGP/Inline as encryption method, make sure "Only download attachments when opened" is checked, see the pictures below