Uhm. I set the email app to check for mail every 30 minutes. But also I don't get that many messages (and mailinglists and whatnot are filtered away to subfolders that don't trigger the notification) so when I get the notification is for something I actually need.

Apart from that I only have notifications for IM (telegram/whatsapp) and the phone is in constant DND mode (with sound allowed only for calls).