I have been using my current email accounts for a long time and never made time to tidy things up. Today when I took a look at things in Mail it is a real mess. My IMAP account appears to have a 'Deleted Messages' folder and a 'Trash' folder one used by my phone, the other by my computer. In the same way, I have a 'Sent' folder and a 'Sent Messages' folder. How do I get both devices using the same one, so I can safely delete the other?