A hardcover book, 365 pages, one out-of-office message per page. Each one calm, professional, and impossible to argue with. "I am away from my desk until Monday and will not be checking messages." "I am in a focus block and will reply this afternoon." "I am unavailable." You have never sent a single one of them. The book does not judge you for that.
Read one a day. Consider sending it. Do not. Keep reading.
Part of The Control Room, for those who can't see what's working.