I changed the season break from 1 to 2, then to 3. Each time I was told that the managers in the league were sent a mail informing them. I did not receive a mail and do not believe any other manager in the league did.
The mail is only sent when the promotion/relegation zones are enabled or disabled, or race time or duration is changed. The text should perhaps be more clear, but it isn't saying a mail is always sent, only if there is some relevant information.