On IOS - I turn off mail, on Mac- go offline from Mail App
On my iPhone/Ipad I usually turn off Email. Go to Settings->Mail and select the Account and turn off only email. I keep contacts and notes still on.
I only turn them back on when I am travelling. This way it keeps me focused and not always picking up the phone when I hear the sound.
On Mac- I have the email client open but it is on offline mode ( Right click on the account and select Take Account Offline).
The emails I write I save them as drafts and at predefined times I go on line (6 am, 10 am, 2 pm and 5 pm- inbox zero), send everything and collect/process what has been accumulated...