Mail pops up randomly
This is getting annoying and I haven't figured out how to disable it.
I recently upgraded to El Capitan.
Since this time, while I am working on stuff, Mail opens (sometimes to the front) and interrupts what I am doing.
Previously in other OS versions it would either stay in the dock or operating in the background (window closed) until I was ready to check mail. Now it just randomly pops up.
Is there a way to stop this happening without having to quit Mail?
This happens on both my iMac and MBP.
Thanks
MacBook Pro, OS X El Capitan (10.11.5), 17 2.4ghz i7