Sometimes the lack of detail or the wording and other factors in enquiries from your website can make it end up in spam, gmail seems particularly guilty of this.
Here is a filter that you can put in place to ensure that website enquiries always end up in your main important emails.
Search for emails with the subject being some words that are always in your email enquiries eg. “New submission from”
and on the filter page tick the box to ‘Never send it to Spam’ and ‘Always mark it as important’.
That should make it a lot less likely that you will miss an important enquiry from your website.