+1 for login items.Try preferences > users and groups > login items.
Is mail there?
No mail is not in there, so will try deleting some login items (this by the way has also been suggested on Apple Communities),Try preferences > users and groups > login items.
Is mail there?
No the box to reopen windows when logging in is not checked.Choose "Log Out" from the Apple menu and see if the check box for "reopen windows when logging back in" is ticked.
What happens if you close all apps, and allow re-open windows on log in?
This may re-set things, but its a guess....
No the box to reopen windows when logging in is not checked.
Switched the mac on this morning and there was the mail desktop again, and I only have "dropbox' ticked in login.
Yes tried that.have you tried this?
Yes I have completely removed the items using the -.It's not what's ticked in the login preferences. The tick just tells the app to open in silent mode. If mail is in the list (ticked or not) you need to remove it.
Select it and click the - button.