Incoming mail doesn't arrive in any application if the application is not open. What's more, especially with an IMAP account, mail can be read in either or both applications. (It's a little more complicated with a POP account. You have to be sure, in Preferences, that that the application tells the server not to delete messages after they are downloaded.) But if you don't want to use Mail, then never launch Mail. Messages cannot arrive in Mail if it is not running.
I have recently installed MS Office on my Mac Book Pro and want to use Outlook as the default mail provider.
All seems fine for outgoing mail, it sends fine but incoming mail arrives in Mac Mail not Outlook, despite ticking the default mail setting button in Outlook Preferences....it seems that Mac Mail is overriding outlook!
Sure I'm doing something silly....what do you think ??
Thanks in advance.