I have 3 email accounts. On my Samsung phone I go into email inbox and I can select either a single email account listed in my inbox or I can select All accounts which I always do. Then any incoming mail from any account is always shown in my inbox.
There is no problem looking at a 3 accounts on my Inbox list using the phone.
However, on my laptop when I log into my email list and it only shows emails from one account and I can find no option to select All accounts.