"Operation restricted due to excessive usage"

"Operation restricted due to excessive usage"

I've logged in this morning and I've got the above message.
I'm pretty sure I wasn't using it excessively...

Also, I have a "ghost" e-mail for a couple of days now.
In the left panel, there's the notification of unread e-mail (Inbox or Unread) but when I want check it there's no new/unread e-mail appears in the right panel.

The message was gone while I was righting this report...

Anyway, the dangling e-mail is still there.

Can you check it, please? It's a little bit confusing.

Thanks in advance,
LI