I use Mail as my primary email software.

In Mail I have 3 accounts:
iCloud (I don't really use this account)
Exchange (this is a work account…and I don't know if this the proper term to use; we use Outlook at work)
Gmail (my primary, private email account)

Everything works seamlessly and I seldom have any problems. However, I notice that often my Exchange account does not show any mails. For example, as I am writing this, it shows that I have 4 unread mails in the Exchange account. However, when I click on the Exchange mailbox no emails appear. The "sender" window is empty and so is the message window. There is not 1 mail shown; neither new nor old.

If I restart Mail then the Exchange mailbox shows all my new and old emails.

So, is there something wrong on my end?