One common reason for this is that your senders email has ended up in the spam quarantine.
By default all accounts have the Spam Experts filter installed with a conservative setting on the “Quarantine threshold”. This is not perfect however and occasionally emails will get flagged incorrectly.
What you need to do is log in to your CPanel account and look for the button to access Spam Experts. It looks something like this:
Once you are in there, look for this page:
Search through those emails and see if you can find the one you are missing.
You also have the option to “Release and Train” the spam filter service amongst others:
Give that a try at least, if it is still missing then there are other things to check. Let us know and we can help out too!