Mail push notification do not work

iPhone 7 Plus (32 GB Silver) iOs 12.1.2

hello together,

I hope you can help me.

On the above mentioned device the mail notification does not work anymore or not for all connected mail accounts.

What already done and checked:

- reinstall the mail app and install again.

- internet connection is good (for the gmail account for example the notification works)

- do not disturp is switched off

- Passwords & Accounts > mail account synchronization is allowed

- Passwords & Accounts> fetch new data -> push is enabled for affected mail account.

My question to you now would be which settings I could still check about.

Thanks for your help