Many people claim to suffer anxiety and stress from something called email overload.
Nobody reported suffering from overload when email became popular a few decades ago. One cause of this alleged overload is the amount of email received, most of which is noise. Much of the noise is resolved using filters.
A notable cause of this alleged stress is instant messaging (IM). When IM became popular many people wrongly attached the same expectations to email. Many people expected and demanded instant replies. Many people treated email the same as IM.
Email never was designed nor intended to be instantaneous or real-time.
Throw away the false premise. Treat email like snail mail. Hope for a timely reply but not an immediate or instant reply. Be prepared for no reply at all.
Important is not running email clients 24/7. There is no need to fear missing out. Emails will wait peacefully in the In Box. Check and reply to email at predetermined times of the day. The world is not going anywhere.