No Incoming Mail

Hello!
I just noticed that my Zoho mail account is not receiving any incoming mail. When I logged in online, it said the last new message was received 5 days ago. I am not receiving any error messages and I can send out mail just fine. This is the first time I have encountered a problem like this. I am not exactly sure what's going on since I am not receiving any error messages when I try to send or receive mail. Any ideas what could be going on?
Thank you!